ProxyBoys

Stunnel Proxy Server

• November 16, 2021
• 0

stunnel TLS Proxy

stunnel TLS Proxy
NAME
SYNOPSIS
DESCRIPTION
OPTIONS
CONFIGURATION FILE
GLOBAL OPTIONS
SERVICE-LEVEL OPTIONS
RETURN VALUE
SIGNALS
EXAMPLES
NOTES
RESTRICTIONS
INETD MODE
CERTIFICATES
RANDOMNESS
DH PARAMETERS
FILES
BUGS
SEE ALSO
AUTHOR
stunnel – TLS offloading and load-balancing proxy
Unix:
stunnel [FILE] | -fd N | -help | -version | -sockets | -options
WIN32:
stunnel [ [ -install | -uninstall | -start | -stop | -reload | -reopen | -exit] [-quiet] [FILE]] | -help | -version | -sockets | -options
The stunnel program is designed to work as TLS encryption wrapper between remote clients and local (inetd-startable) or remote servers. The concept is that having non-TLS aware daemons running on your system you can easily set them up to communicate with clients over secure TLS channels.
stunnel can be used to add TLS functionality to commonly used Inetd daemons like POP-2, POP-3, and IMAP servers, to standalone daemons like NNTP, SMTP and HTTP, and in tunneling PPP over network sockets without changes to the source code.
This product includes cryptographic software written by Eric Young ()
FILE
Use specified configuration file
-fd N (Unix only)
Read the config file from specified file descriptor
-help
Print stunnel help menu
-version
Print stunnel version and compile time defaults
-sockets
Print default socket options
-options
Print supported TLS options
-install (Windows NT and later only)
Install NT Service
-uninstall (Windows NT and later only)
Uninstall NT Service
-start (Windows NT and later only)
Start NT Service
-stop (Windows NT and later only)
Stop NT Service
-reload (Windows NT and later only)
Reload the configuration file of the running NT Service
-reopen (Windows NT and later only)
Reopen the log file of the running NT Service
-exit (Win32 only)
Exit an already started stunnel
-quiet (Win32 only)
Don’t display any message boxes
Each line of the configuration file can be either:
An empty line (ignored).
A comment starting with ‘;’ (ignored).
An ‘option_name = option_value’ pair.
‘[service_name]’ indicating a start of a service definition.
An address parameter of an option may be either:
A port number.
A colon-separated pair of IP address (either IPv4, IPv6, or domain name) and port number.
A Unix socket path (Unix only).
chroot = DIRECTORY (Unix only)
directory to chroot stunnel process
chroot keeps stunnel in a chrooted jail. CApath, CRLpath, pid and exec are located inside the jail and the patches have to be relative to the directory specified with chroot.
Several functions of the operating system also need their files to be located within the chroot jail, e. g. :
Delayed resolver typically needs /etc/ and /etc/
Local time in log files needs /etc/timezone.
Some other functions may need devices, e. /dev/zero or /dev/null.
compression = deflate | zlib
select data compression algorithm
default: no compression
Deflate is the standard compression method as described in RFC 1951.
debug = [FACILITY. ]LEVEL
debugging level
Level is one of the syslog level names or numbers emerg (0), alert (1), crit (2), err (3), warning (4), notice (5), info (6), or debug (7). All logs for the specified level and all levels numerically less than it will be shown. Use debug = debug or debug = 7 for greatest debugging output. The default is notice (5).
The syslog facility ‘daemon’ will be used unless a facility name is supplied. (Facilities are not supported on Win32. )
Case is ignored for both facilities and levels.
EGD = EGD_PATH (Unix only)
path to Entropy Gathering Daemon socket
Entropy Gathering Daemon socket to use to feed the OpenSSL random number generator.
engine = auto | ENGINE_ID
select hardware or software cryptographic engine
default: software-only cryptography
See Examples section for an engine configuration to use the certificate and the corresponding private key from a cryptographic device.
engineCtrl = COMMAND[:PARAMETER]
control hardware engine
engineDefault = TASK_LIST
set OpenSSL tasks delegated to the current engine
The parameter specifies a comma-separated list of task to be delegated to the current engine.
The following tasks may be available, if supported by the engine: ALL, RSA, DSA, ECDH, ECDSA, DH, RAND, CIPHERS, DIGESTS, PKEY, PKEY_CRYPTO, PKEY_ASN1.
fips = yes | no
enable or disable FIPS 140-2 mode.
This option allows you to disable entering FIPS mode if stunnel was compiled with FIPS 140-2 support.
default: no (since version 5. 00)
foreground = yes | quiet | no (Unix only)
foreground mode
Stay in foreground (don’t fork).
With the yes parameter it also logs to stderr in addition to the destinations specified with syslog and output.
default: background in daemon mode
iconActive = ICON_FILE (GUI only)
GUI icon to be displayed when there are established connections
On Windows platform the parameter should be an file containing a 16×16 pixel image.
iconError = ICON_FILE (GUI only)
GUI icon to be displayed when no valid configuration is loaded
iconIdle = ICON_FILE (GUI only)
GUI icon to be displayed when there are no established connections
log = append | overwrite
log file handling
This option allows you to choose whether the log file (specified with the output option) is appended or overwritten when opened or re-opened.
default: append
output = FILE
append log messages to a file
/dev/stdout device can be used to send log messages to the standard output (for example to log them with daemontools splogger).
pid = FILE (Unix only)
pid file location
If the argument is empty, then no pid file will be created.
pid path is relative to the chroot directory if specified.
RNDbytes = BYTES
bytes to read from random seed files
RNDfile = FILE
path to file with random seed data
The OpenSSL library will use data from this file first to seed the random number generator.
RNDoverwrite = yes | no
overwrite the random seed files with new random data
default: yes
service = SERVICE (Unix only)
stunnel service name
The specified service name is used for syslog and as the inetd mode service name for TCP Wrappers. While this option can technically be specified in the service sections, it is only useful in global options.
default: stunnel
syslog = yes | no (Unix only)
enable logging via syslog
taskbar = yes | no (WIN32 only)
enable the taskbar icon
Each configuration section begins with a service name in square brackets. The service name is used for libwrap (TCP Wrappers) access control and lets you distinguish stunnel services in your log files.
Note that if you wish to run stunnel in inetd mode (where it is provided a network socket by a server such as inetd, xinetd, or tcpserver) then you should read the section entitled INETD MODE below.
accept = [HOST:]PORT
accept connections on specified address
If no host specified, defaults to all IPv4 addresses for the local host.
To listen on all IPv6 addresses use:
accept =:::PORT
CApath = DIRECTORY
Certificate Authority directory
This is the directory in which stunnel will look for certificates when using the verifyChain or verifyPeer options. Note that the certificates in this directory should be named XXXXXXXX. 0 where XXXXXXXX is the hash value of the DER encoded subject of the cert.
The hash algorithm has been changed in OpenSSL 1. 0. It is required to c_rehash the directory on upgrade from OpenSSL 0. x. x to OpenSSL 1. x.
CApath path is relative to the chroot directory if specified.
CAfile = CA_FILE
Certificate Authority file
This file contains multiple CA certificates, to be used with the verifyChain and verifyPeer options.
cert = CERT_FILE
certificate chain file name
The parameter specifies the file containing certificates used by stunnel to authenticate itself against the remote client or server. The file should contain the whole certificate chain starting from the actual server/client certificate, and ending with the self-signed root CA certificate. The file must be either in PEM or P12 format.
A certificate chain is required in server mode, and optional in client mode.
This parameter is also used as the certificate identifier when a hardware engine is enabled.
checkEmail = EMAIL
email address of the peer certificate subject
Multiple checkEmail options are allowed in a single service section. Certificates are accepted if no subject checks were specified, or the email address of the peer certificate matches any of the email addresses specified with checkEmail.
This option requires OpenSSL 1. 2 or later.
checkHost = HOST
host of the peer certificate subject
Multiple checkHost options are allowed in a single service section. Certificates are accepted if no subject checks were specified, or the host name of the peer certificate matches any of the hosts specified with checkHost.
checkIP = IP
IP address of the peer certificate subject
Multiple checkIP options are allowed in a single service section. Certificates are accepted if no subject checks were specified, or the IP address of the peer certificate matches any of the IP addresses specified with checkIP.
ciphers = CIPHER_LIST
select permitted TLS ciphers (TLSv1. 2 and below)
This option does not impact TLSv1. 3 ciphersuites.
A colon-delimited list of the ciphers to allow in the TLS connection, for example DES-CBC3-SHA:IDEA-CBC-MD5.
ciphersuites = CIPHERSUITES_LIST
select permitted TLSv1. 3 ciphersuites
A colon-delimited list of TLSv1. 3 ciphersuites names in order of preference.
This option requires OpenSSL 1. 1. 1 or later.
default: TLS_CHACHA20_POLY1305_SHA256:TLS_AES_256_GCM_SHA384:TLS_AES_128_GCM_SHA256
client = yes | no
client mode (remote service uses TLS)
default: no (server mode)
config = COMMAND[:PARAMETER]
OpenSSL configuration command
The OpenSSL configuration command is executed with the specified parameter. This allows any configuration commands to be invoked from the stunnel configuration file. Supported commands are described on the SSL_CONF_cmd(3ssl) manual page.
Several config lines can be used to specify multiple configuration commands.
Use curves option instead of enabling config = Curves:list_curves to support elliptic curves.
connect = [HOST:]PORT
connect to a remote address
If no host is specified, the host defaults to localhost.
Multiple connect options are allowed in a single service section.
If host resolves to multiple addresses and/or if multiple connect options are specified, then the remote address is chosen using a round-robin algorithm.
CRLpath = DIRECTORY
Certificate Revocation Lists directory
This is the directory in which stunnel will look for CRLs when using the verifyChain and verifyPeer options. Note that the CRLs in this directory should be named XXXXXXXX. r0 where XXXXXXXX is the hash value of the CRL.
CRLpath path is relative to the chroot directory if specified.
CRLfile = CRL_FILE
Certificate Revocation Lists file
This file contains multiple CRLs, used with the verifyChain and verifyPeer options.
curves = list
ECDH curves separated with ‘:’
Only a single curve name is allowed for OpenSSL older than 1. 1.
To get a list of supported curves use:
openssl ecparam -list_curves
default:
X25519:P-256:X448:P-521:P-384 (OpenSSL 1. 1 or later)
prime256v1 (OpenSSL older than 1. 1)
logId = TYPE
connection identifier type
This identifier allows you to distinguish log entries generated for each of the connections.
Currently supported types:
sequential
The numeric sequential identifier is only unique within a single instance of stunnel, but very compact. It is most useful for manual log analysis.
unique
This alphanumeric identifier is globally unique, but longer than the sequential number. It is most useful for automated log analysis.
thread
The operating system thread identifier is neither unique (even within a single instance of stunnel) nor short. It is most useful for debugging software or configuration issues.
process
The operating system process identifier (PID) may be useful in the inetd mode.
default: sequential
debug = LEVEL
Level is a one of the syslog level names or numbers emerg (0), alert (1), crit (2), err (3), warning (4), notice (5), info (6), or debug (7). The default is notice (5).
While the debug = debug or debug = 7 level generates the most verbose output, it is only intended to be used by stunnel developers. Please only use this value if you are a developer, or you intend to send your logs to our technical support. Otherwise, the generated logs will be confusing.
delay = yes | no
delay DNS lookup for the connect option
This option is useful for dynamic DNS, or when DNS is not available during stunnel startup (road warrior VPN, dial-up configurations).
Delayed resolver mode is automatically engaged when stunnel fails to resolve on startup any of the connect targets for a service.
Delayed resolver inflicts failover = prio.
default: no
engineId = ENGINE_ID
select engine ID for the service
engineNum = ENGINE_NUMBER
select engine number for the service
The engines are numbered starting from 1.
exec = EXECUTABLE_PATH
execute a local inetd-type program
exec path is relative to the chroot directory if specified.
The following environmental variables are set on Unix platforms: REMOTE_HOST, REMOTE_PORT, SSL_CLIENT_DN, SSL_CLIENT_I_DN.
execArgs = $0 $1 $2…
arguments for exec including the program name ($0)
Quoting is currently not supported. Arguments are separated with an arbitrary amount of whitespace.
failover = rr | prio
Failover strategy for multiple “connect” targets.
rr
round robin – fair load distribution
prio
priority – use the order specified in config file
default: prio
ident = USERNAME
use IDENT (RFC 1413) username checking
include = DIRECTORY
include all configuration file parts located in DIRECTORY
The files are included in the ascending alphabetical order of their names. The recommended filename convention is
for global options:
for local service-level options:
key = KEY_FILE
private key for the certificate specified with cert option
A private key is needed to authenticate the certificate owner. Since this file should be kept secret it should only be readable by its owner. On Unix systems you can use the following command:
chmod 600 keyfile
This parameter is also used as the private key identifier when a hardware engine is enabled.
default: the value of the cert option
libwrap = yes | no
Enable or disable the use of /etc/ and /etc/
local = HOST
By default, the IP address of the outgoing interface is used as the source for remote connections. Use this option to bind a static local IP address instead.
OCSP = URL
select OCSP responder for certificate verification
OCSPaia = yes | no
validate certificates with their AIA OCSP responders
This option enables stunnel to validate certificates with the list of OCSP responder URLs retrieved from their AIA (Authority Information Access) extension.
OCSPflag = OCSP_FLAG
specify OCSP responder flag
Several OCSPflag can be used to specify multiple flags.
currently supported flags: NOCERTS, NOINTERN, NOSIGS, NOCHAIN, NOVERIFY, NOEXPLICIT, NOCASIGN, NODELEGATED, NOCHECKS, TRUSTOTHER, RESPID_KEY, NOTIME
OCSPnonce = yes | no
send and verify the OCSP nonce extension
This option protects the OCSP protocol against replay attacks. Due to its computational overhead, the nonce extension is usually only supported on internal (e. corporate) responders, and not on public OCSP responders.
options = SSL_OPTIONS
OpenSSL library options
The parameter is the OpenSSL option name as described in the SSL_CTX_set_options(3ssl) manual, but without SSL_OP_ prefix. stunnel -options lists the options found to be allowed in the current combination of stunnel and the OpenSSL library used to build it.
Several option lines can be used to specify multiple options. An option name can be prepended with a dash (“-“) to disable the option.
For example, for compatibility with the erroneous Eudora TLS implementation, the following option can be used:
options = DONT_INSERT_EMPTY_FRAGMENTS
options = NO_SSLv2
options = NO_SSLv3
Use sslVersionMax or sslVersionMin option instead of disabling specific TLS protocol versions when compiled with OpenSSL 1. 0 or later.
protocol = PROTO
application protocol to negotiate TLS
This option enables initial, protocol-specific negotiation of the TLS encryption. The protocol option should not be used with TLS encryption on a separate port.
Currently supported protocols:
cifs
Proprietary (undocummented) extension of CIFS protocol implemented in Samba. Support for this extension was dropped in Samba 3. 0.
connect
Based on RFC 2817 – Upgrading to TLS Within HTTP/1. 1, section 5. 2 – Requesting a Tunnel with CONNECT
This protocol is only supported in client mode.
imap
Based on RFC 2595 – Using TLS with IMAP, POP3 and ACAP
ldap
Based on RFC 2830 – Lightweight Directory Access Protocol (v3): Extension for Transport Layer Security
nntp
Based on RFC 4642 – Using Transport Layer Security (TLS) with Network News Transfer Protocol (NNTP)
pgsql
Based on
pop3
Based on RFC 2449 – POP3 Extension Mechanism
proxy
Passing of the original client IP address with HAProxy PROXY protocol version 1
smtp
Based on RFC 2487 – SMTP Service Extension for Secure SMTP over TLS
socks
SOCKS versions 4, 4a, and 5 are supported. The SOCKS protocol itself is encapsulated within TLS encryption layer to protect the final destination address.
The BIND command of the SOCKS protocol is not supported. The USERID parameter is ignored.
See Examples section for sample configuration files for VPN based on SOCKS encryption.
protocolAuthentication = AUTHENTICATION
authentication type for the protocol negotiations
Currently, this option is only supported in the client-side ‘connect’ and ‘smtp’ protocols.
Supported authentication types for the ‘connect’ protocol are ‘basic’ or ‘ntlm’. The default ‘connect’ authentication type is ‘basic’.
Supported authentication types for the ‘smtp’ protocol are ‘plain’ or ‘login’. The default ‘smtp’ authentication type is ‘plain’.
protocolDomain = DOMAIN
domain for the protocol negotiations
Currently, this option is only supported in the client-side ‘connect’ protocol.
header for the protocol negotiations
protocolHost = ADDRESS
host address for the protocol negotiations
For the ‘connect’ protocol negotiations, protocolHost specifies HOST:PORT of the final TLS server to be connected to by the proxy. The proxy server directly connected by stunnel must be specified with the connect option.
For the ‘smtp’ protocol negotiations, protocolHost controls the client SMTP HELO/EHLO value.
protocolPassword = PASSWORD
password for the protocol negotiations
protocolUsername = USERNAME
username for the protocol negotiations
PSKidentity = IDENTITY
PSK identity for the PSK client
PSKidentity can be used on stunnel clients to select the PSK identity used for authentication. This option is ignored in server sections.
default: the first identity specified in the PSKsecrets file.
PSKsecrets = FILE
file with PSK identities and corresponding keys
Each line of the file in the following format:
IDENTITY:KEY
Hexadecimal keys are automatically converted to binary form. Keys are required to be at least 16 bytes long, which implies at least 32 characters for hexadecimal keys. The file should neither be world-readable nor world-writable.
pty = yes | no (Unix only)
allocate a pseudoterminal for ‘exec’ option
redirect = [HOST:]PORT
redirect TLS client connections on certificate-based authentication failures
This option only works in server mode. Some protocol negotiations are also incompatible with the redirect option.
renegotiation = yes | no
support TLS renegotiation
Applications of the TLS renegotiation include some authentication scenarios, or re-keying long lasting connections.
On the other hand this feature can facilitate a trivial CPU-exhaustion DoS attack:
Please note that disabling TLS renegotiation does not fully mitigate this issue.
default: yes (if supported by OpenSSL)
reset = yes | no
attempt to use the TCP RST flag to indicate an error
This option is not supported on some platforms.
retry = yes | no
reconnect a connect+exec section after it was disconnected
securityLevel = LEVEL
set the security level
The meaning of each level is described below:
level 0
Everything is permitted.
level 1
The security level corresponds to a minimum of 80 bits of security. Any parameters offering below 80 bits of security are excluded. As a result RSA, DSA and DH keys shorter than 1024 bits and ECC keys shorter than 160 bits are prohibited. All export cipher suites are prohibited since they all offer less than 80 bits of security. SSL version 2 is prohibited. Any cipher suite using MD5 for the MAC is also prohibited.
level 2
Security level set to 112 bits of security. As a result RSA, DSA and DH keys shorter than 2048 bits and ECC keys shorter than 224 bits are prohibited. In addition to the level 1 exclusions any cipher suite using RC4 is also prohibited. SSL version 3 is also not allowed. Compression is disabled.
level 3
Security level set to 128 bits of security. As a result RSA, DSA and DH keys shorter than 3072 bits and ECC keys shorter than 256 bits are prohibited. In addition to the level 2 exclusions cipher suites not offering forward secrecy are prohibited. TLS versions below 1. 1 are not permitted. Session tickets are disabled.
level 4
Security level set to 192 bits of security. As a result RSA, DSA and DH keys shorter than 7680 bits and ECC keys shorter than 384 bits are prohibited. Cipher suites using SHA1 for the MAC are prohibited. 2 are not permitted.
level 5
Security level set to 256 bits of security. As a result RSA, DSA and DH keys shorter than 15360 bits and ECC keys shorter than 512 bits are prohibited.
default: 2
The securityLevel option is only available when compiled with OpenSSL 1. 0 and later.
requireCert = yes | no
require a client certificate for verifyChain or verifyPeer
With requireCert set to no, the stunnel server accepts client connections that did not present a certificate.
Both verifyChain = yes and verifyPeer = yes imply requireCert = yes.
setgid = GROUP (Unix only)
Unix group id
As a global option: setgid() to the specified group in daemon mode and clear all other groups.
As a service-level option: set the group of the Unix socket specified with “accept”.
setuid = USER (Unix only)
Unix user id
As a global option: setuid() to the specified user in daemon mode.
As a service-level option: set the owner of the Unix socket specified with “accept”.
sessionCacheSize = NUM_ENTRIES
session cache size
sessionCacheSize specifies the maximum number of the internal session cache entries.
The value of 0 can be used for unlimited size. It is not recommended for production use due to the risk of a memory exhaustion DoS attack.
sessionCacheTimeout = TIMEOUT
session cache timeout
This is the number of seconds to keep cached TLS sessions.
sessionResume = yes | no
allow or disallow session resumption
sessiond = HOST:PORT
address of sessiond TLS cache server
sni = SERVICE_NAME:SERVER_NAME_PATTERN (server mode)
Use the service as a slave service (a name-based virtual server) for Server Name Indication TLS extension (RFC 3546).
SERVICE_NAME specifies the master service that accepts client connections with the accept option. SERVER_NAME_PATTERN specifies the host name to be redirected. The pattern may start with the ‘*’ character, e. ‘*. ‘. Multiple slave services are normally specified for a single master service. The sni option can also be specified more than once within a single slave service.
This service, as well as the master service, may not be configured in client mode.
The connect option of the slave service is ignored when the protocol option is specified, as protocol connects to the remote host before TLS handshake.
Libwrap checks (Unix only) are performed twice: with the master service name after TCP connection is accepted, and with the slave service name during the TLS handshake.
The sni option is only available when compiled with OpenSSL 1. 0 and later.
sni = SERVER_NAME (client mode)
Use the parameter as the value of TLS Server Name Indication (RFC 3546) extension.
Empty SERVER_NAME disables sending the SNI extension.
socket = a|l|r:OPTION=VALUE[:VALUE]
Set an option on the accept/local/remote socket
The values for the linger option are l_onof:l_linger. The values for the time are tv_sec:tv_usec.
Examples:
socket = l_SO_LINGER=1:60
set one minute timeout for closing local socket
socket = r_SO_OOBINLINE=yes
place out-of-band data directly into the
receive data stream for remote sockets
socket = a_SO_REUSEADDR=no
disable address reuse (enabled by default)
socket = a_SO_BINDTODEVICE=lo
only accept connections on loopback interface
sslVersion = SSL_VERSION
select the TLS protocol version
Supported versions: all, SSLv2, SSLv3, TLSv1, TLSv1. 1, TLSv1. 2, TLSv1. 3
Availability of specific protocols depends on the linked OpenSSL library. Older versions of OpenSSL do not support TLSv1. 2 and TLSv1. 3. Newer versions of OpenSSL do not support SSLv2.
Obsolete SSLv2 and SSLv3 are currently disabled by default.
Setting the option
is equivalent to options
sslVersionMax = SSL_VERSION
sslVersionMin = SSL_VERSION
when compiled with OpenSSL 1. 0 and later.
maximum supported protocol versions
Supported versions: all, SSLv3, TLSv1, TLSv1. 3
all enable protocol versions up to the highest version supported by the linked OpenSSL library.
Availability of specific protocols depends on the linked OpenSSL library.
The sslVersionMax option is only available when compiled with OpenSSL 1. 0 and later.
default: all
minimum supported protocol versions
all enable protocol versions down to the lowest version supported by the linked OpenSSL library.
The sslVersionMin option is only available when compiled with OpenSSL 1. 0 and later.
default: TLSv1
stack = BYTES (except for FORK model)
CPU stack size of created threads
Excessive thread stack size increases virtual memory usage. Insufficient thread stack size may cause application crashes.
default: 65536 bytes (sufficient for all platforms we tested)
ticketKeySecret = SECRET
hexadecimal symmetric key used for session ticket confidentiality protection
Session tickets defined in RFC 5077 provide an enhanced session resumption capability, where the server-side caching is not required to maintain per session state.
Combining ticketKeySecret and ticketMacSecret options allow to resume a negotiated session on other cluster nodes, or to resume a negotiated session after server restart.
The key is required to be either 16 or 32 bytes long, which implies exactly 32 or 64 hexadecimal digits. Colons may optionally be used between two-character hexadecimal bytes.
This option only works in server mode.
The ticketKeySecret option is only available when compiled with OpenSSL 1. 0 and later.
Disabling NO_TICKET option is required for the ticket support in OpenSSL older than 1. 1, but note that this option is incompatible with the redirect option.
ticketMacSecret = SECRET
hexadecimal symmetric key used for session ticket integrity protection
The ticketMacSecret option is only available when compiled with OpenSSL 1. 0 and later.
TIMEOUTbusy = SECONDS
time to wait for expected data
TIMEOUTclose = SECONDS
time to wait for close_notify (set to 0 for buggy MSIE)
TIMEOUTconnect = SECONDS
time to wait to connect to a remote host
TIMEOUTidle = SECONDS
time to keep an idle connection
transparent = none | source | destination | both (Unix only)
enable transparent proxy support on selected platforms
Supported values:
none
Disable transparent proxy support. This is the default.
source
Re-write the address to appear as if a wrapped daemon is connecting from the TLS client machine instead of the machine running stunnel.
This option is currently available in:
Remote mode (connect option) on Linux >=2. 6. 28
This configuration requires stunnel to be executed as root and without the setuid option.
This configuration requires the following setup for iptables and routing (possibly in /etc/ or equivalent file):
iptables -t mangle -N DIVERT
iptables -t mangle -A PREROUTING -p tcp -m socket -j DIVERT
iptables -t mangle -A DIVERT -j MARK –set-mark 1
iptables -t mangle -A DIVERT -j ACCEPT
ip rule add fwmark 1 lookup 100
ip route add local 0. 0/0 dev lo table 100
echo 0 >/proc/sys/net/ipv4/conf/lo/rp_filter
stunnel must also to be executed as root and without the setuid option.
Remote mode (connect option) on Linux 2. 2. x
This configuration requires the kernel to be compiled with the transparent proxy option. Connected service must be installed on a separate host. Routing towards the clients has to go through the stunnel box.
Remote mode (connect option) on FreeBSD >=8. 0
This configuration requires additional firewall and routing setup. stunnel must also to be executed as root and without the setuid option.
Local mode (exec option)
This configuration works by pre-loading the shared library. _RLD_LIST environment variable is used on Tru64, and LD_PRELOAD variable on other platforms.
destination
The original destination is used instead of the connect option.
A service section for transparent destination may look like this:
[transparent]
client = yes
accept =
transparent = destination
This configuration requires iptables setup to work, possibly in /etc/ or equivalent file.
For a connect target installed on the same host:
/sbin/iptables -t nat -I OUTPUT -p tcp –dport
-m! –uid-owner
-j DNAT –to-destination :
For a connect target installed on a remote host:
/sbin/iptables -I INPUT -i eth0 -p tcp –dport -j ACCEPT
/sbin/iptables -t nat -I PREROUTING -p tcp –dport
-i eth0 -j DNAT –to-destination :
The transparent destination option is currently only supported on Linux.
both
Use both source and destination transparent proxy.
Two legacy options are also supported for backward compatibility:
yes
This option has been renamed to source.
no
This option has been renamed to none.
verify = LEVEL
verify the peer certificate
This option is obsolete and should be replaced with the verifyChain and verifyPeer options.
Request and ignore the peer certificate.
Verify the peer certificate if present.
Verify the peer certificate.
Verify the peer against a locally installed certificate.
Ignore the chain and only verify the peer certificate.
default
No verify.
verifyChain = yes | no
verify the peer certificate chain starting from the root CA
For server certificate verification it is essential to also require a specific certificate with checkHost or checkIP.
The self-signed root CA certificate needs to be stored either in the file specified with CAfile, or in the directory specified with CApath.
verifyPeer = yes | no
The peer certificate needs to be stored either in the file specified with CAfile, or in the directory specified with CApath.
stunnel returns zero on success, non-zero on error.
The following signals can be used to control stunnel in Unix environment:
SIGHUP
Force a reload of the configuration file.
Some global options will not be reloaded:
chroot
foreground
pid
setgid
setuid
The use of the ‘setuid’ option will also prevent stunnel from binding to privileged (<1024) ports during configuration reloading. When the 'chroot' option is used, stunnel will look for all its files (including the configuration file, certificates, the log file and the pid file) within the chroot jail. SIGUSR1 Close and reopen the stunnel log file. This function can be used for log rotation. SIGUSR2 Log the list of active connections. SIGTERM, SIGQUIT, SIGINT Shut stunnel down. The result of sending any other signals to the server is undefined. In order to provide TLS encapsulation to your local imapd service, use: [imapd] accept = 993 exec = /usr/sbin/imapd execArgs = imapd or in remote mode: connect = 143 In order to let your local e-mail client connect to a TLS-enabled imapd service on another server, configure the e-mail client to connect to localhost on port 119 and use: [imap] accept = 143 connect = servername:993 If you want to provide tunneling to your pppd daemon on port 2020, use something like: [vpn] accept = 2020 exec = /usr/sbin/pppd execArgs = pppd local pty = yes If you want to use stunnel in inetd mode to launch your imapd process, you'd use this Note there must b

Stunnel – Wikipedia

stunnelDeveloper(s)Michał TrojnaraInitial release10 December 1998; 22 years ago[citation needed]Stable release5. 60
/ 16 August 2021; 2 months ago[1]Repository inC[2]Operating systemMulti-platformTypeProxy, EncryptionLicenseGNU General Public LicenseWebsite
Stunnel is an open-source multi-platform application used to provide a universal TLS/SSL tunneling service.
Stunnel can be used to provide secure encrypted connections for clients or servers that do not speak TLS or SSL natively. [3] It runs on a variety of operating systems, [4] including most Unix-like operating systems and Windows. Stunnel relies on the OpenSSL library to implement the underlying TLS or SSL protocol.
Stunnel uses public-key cryptography with X. 509 digital certificates to secure the SSL connection, and clients can optionally be authenticated via a certificate. [5]
If linked against libwrap, it can be configured to act as a proxy–firewall service as well.
Stunnel is maintained by Michał Trojnara and released under the terms of the GNU General Public License (GPL) with OpenSSL exception.
Example scenario[edit]
For example, one could use stunnel to provide a secure SSL connection to an existing non-SSL-aware SMTP mail server. Assuming the SMTP server expects TCP connections on port 25, one would configure stunnel to map the SSL port 465 to non-SSL port 25. A mail client connects via SSL to port 465. Network traffic from the client initially passes over SSL to the stunnel application, which transparently encrypts and decrypts traffic and forwards unsecured traffic to port 25 locally. The mail server sees a non-SSL mail client. [citation needed]
The stunnel process could be running on the same or a different server from the unsecured mail application; however, both machines would typically be behind a firewall on a secure internal network (so that an intruder could not make its own unsecured connection directly to port 25).
See also[edit]
Tunneling protocol
References[edit]
^ Trojnara, Michał. “Downloads”. Stunnel. Retrieved 22 August 2021.
^ Trojnara, Michał. “stunnel sources”. GitHub. Retrieved 12 May 2020.
^ O’Donovan, Barry (October 2004). “Secure Communication with Stunnel”. Linux Gazette, Issue 107.
^ “”stunnel: Ports””. Archived from the original on 1 April 2019. Retrieved 24 August 2020.
^ “stunnel(8) manual”
External links[edit]
Official website

OpenVPN over Stunnel RUT230 – Teltonika Networks Wiki

Main Page > RUT Routers > RUT230 > RUT230 Configuration Examples > OpenVPN over Stunnel RUT230
Introduction[edit source]
Stunnel is an open-source a proxy service that adds TLS encryption to clients and servers already existing on a VPN network. TLS encryption provided by Stunnel can be used as an additional layer of encryption for data sent by OpenVPN. This procedure increases the security of the established connection and provides higher chances of passing a Deep packet inspection (DPI) check.
This article contains instructions on how to configure an OpenVPN over Stunnel topology.
Overview[edit source]
You will need
two routers of the RUTxxx series (except RUT850);
at least one router (server) with a public IP;
TLS certificates for the server and the client (for instructions on generating TLS certificates, click here).
Topology
Explanation
An OpenVPN client is connected to an OpenVPN server (both hosted on RUT routers) via a TLS encrypted Stunnel connection. This provides the possibility to transfer data between remote private networks (LAN A and LAN B) and adds an additional TLS security layer for the connection.
Server configuration[edit source]
First, configure the OpenVPN and Stunnel servers. The Stunnel server will listen for incoming client connections on the specified TCP port (9999 in this example) and connect them to OpenVPN server running on the local host.
The logic of the connection can be visualized like this:
OpenVPN server[edit source]
Navigate to the Services → VPN → OpenVPN page. Select Role: Server, enter a custom name and click the ‘Add New’ button. An OpenVPN server instance with the given name will appear in the “OpenVPN Configuration” list. To begin configuration, click the ‘Edit’ button next to the server instance.
The figure below displays the configuration used for our example. Take note of the comments that are provided next to fields that differ from the default value:
Don’t forget to click the Save button located at the bottom-right side of the page.
Stunnel server[edit source]
Navigate to the Services → VPN → Stunnel page and enable the “Stunnel Globals” configuration:
Click Save.
To create a new Stunnel instance, enter a custom name for it and click the ‘Add’ button. A new instance with the given name will appear in the “Stunnel Configuration” list. To begin configuration, click the ‘Edit’ button next to the instance.
Open Stunnel port[edit source]
The OpenVPN default port (1194) is opened by default. But you will have manually open the select Stunnel port (9999 in this example).
To do this, navigate to the Network → Firewall → Traffic Rules page and scroll down until you see the Open Ports On Router section. Fill out the configuration fields as indicated in the figure above and click the ‘Add’ button:
Client configuration[edit source]
Configure the OpenVPN and Stunnel clients that will be connecting to the server. Unlike in the server, there is reason to configure Stunnel client before the OpenVPN client (the other way around will also work but an OpenVPN service restart may be required) so it is recommended to start with that.
The OpenVPN client will connect to TCP port 1194 of the local host and the Stunnel client will connect to the WAN IP and Stunnel port (192. 168. 10. 1:9999 in this example) of the server router.
The logic of the entire connection can be visualized like this:
Stunnel client[edit source]
OpenVPN client[edit source]
Navigate to the Services → VPN → OpenVPN page. An OpenVPN client instance with the given name will appear in the “OpenVPN Configuration” list. To begin configuration, click the ‘Edit’ button next to the client instance.
Testing and troubleshooting[edit source]
If you have completed the steps presented above, your configuration is complete. This section provides tips on how to test and troubleshoot this OpenVPN over Stunnel connection.
Check whether remote side is reachable by sending ICMP requests. To do that, go to the Services → CLI page. Login (username: root; password: router’s password) and ping the opposite instance:
ping 10. 8. 0. 6Is the response looks like this, then the connection was established successfully:
64 bytes from 10. 6: seq=0 ttl=64 time=101. 214 ms
64 bytes from 10. 6: seq=1 ttl=64 time=91. 018 ms
64 bytes from 10. 6: seq=2 ttl=64 time=88. 974 ms
64 bytes from 10. 6: seq=3 ttl=64 time=502. 781 ms
If there is no response to the ping requests, check whether Stunnel and OpenVPN services are running on the device. For Stunnel use this command:
ps | grep stunnel | grep -v grepThe output should look similar to this:
16122 root 2992 S /usr/bin/stunnel /tmp/
For OpenVPN use this command:
ps | grep openvpn | grep -v grepThe output should look similar to this:
13034 root 3428 S /usr/sbin/openvpn –syslog openvpn(7365727665725F41)
To restart OpenVPN or Stunnel services, use one of these commands:
/etc/init. d/openvpn restart
/etc/init. d/stunnel restart
Double check your configuration. Check for configuration mistakes, see if correct certificate files are uploaded onto each instance, make sure the Stunnel port is not used by another program, etc.

Frequently Asked Questions about stunnel proxy server

What is a Stunnel server?

Stunnel is an open-source multi-platform application used to provide a universal TLS/SSL tunneling service. Stunnel can be used to provide secure encrypted connections for clients or servers that do not speak TLS or SSL natively.

Is stunnel a VPN?

IntroductionEdit. Stunnel is an open-source a proxy service that adds TLS encryption to clients and servers already existing on a VPN network. TLS encryption provided by Stunnel can be used as an additional layer of encryption for data sent by OpenVPN.Jul 10, 2019

How do I set up stunnel?

How to Configure Stunnel WindowsInstall Stunnel. … Copy a valid SSL public certificate to the directory “C:Program Files (x86)stunnel.” To make things more trouble-free, combine the public key and private key certificates into one . … Modify the Stunnel configuration file. … Configure Stunnel to start automatically.