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SSH server & client security auditing (banner, key exchange, encryption, mac, compression, compatibility, security, etc)

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ssh-audit

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ssh-audit is a tool for ssh server & client configuration auditing.

jtesta/ssh-audit (v2.0+) is the updated and maintained version of ssh-audit forked from arthepsy/ssh-audit (v1.x) due to inactivity.

Features

  • SSH1 and SSH2 protocol server support;
  • analyze SSH client configuration;
  • grab banner, recognize device or software and operating system, detect compression;
  • gather key-exchange, host-key, encryption and message authentication code algorithms;
  • output algorithm security information (available since, removed/disabled, unsafe/weak/legacy, etc);
  • output algorithm recommendations (append or remove based on recognized software version);
  • analyze SSH version compatibility based on algorithm information;
  • historical information from OpenSSH, Dropbear SSH and libssh;
  • policy scans to ensure adherence to a hardened/standard configuration;
  • runs on Linux and Windows;
  • supports Python 3.8 - 3.13;
  • no dependencies

Usage

usage: ssh-audit.py [-h] [-1] [-2] [-4] [-6] [-b] [-c] [-d]
                    [-g <min1:pref1:max1[,min2:pref2:max2,...]> / <x-y[:step]>] [-j] [-l {info,warn,fail}] [-L]
                    [-M custom_policy.txt] [-m] [-n] [-P "Built-In Policy Name" / custom_policy.txt] [-p N]
                    [-T targets.txt] [-t N] [-v] [--conn-rate-test N[:max_rate]] [--dheat N[:kex[:e_len]]]
                    [--lookup alg1[,alg2,...]] [--skip-rate-test] [--threads N]
                    [host]

positional arguments:
  host                  target hostname or IPv4/IPv6 address

optional arguments:
  -h, --help            show this help message and exit
  -1, --ssh1            force ssh version 1 only
  -2, --ssh2            force ssh version 2 only
  -4, --ipv4            enable IPv4 (order of precedence)
  -6, --ipv6            enable IPv6 (order of precedence)
  -b, --batch           batch output
  -c, --client-audit    starts a server on port 2222 to audit client software config (use -p to change port; use -t
                        to change timeout)
  -d, --debug           enable debugging output
  -g <min1:pref1:max1[,min2:pref2:max2,...]> / <x-y[:step]>, --gex-test <min1:pref1:max1[,min2:pref2:max2,...]> / <x-y[:step]>
                        conducts a very customized Diffie-Hellman GEX modulus size test. Tests an array of minimum,
                        preferred, and maximum values, or a range of values with an optional incremental step amount
  -j, --json            enable JSON output (use -jj to enable indentation for better readability)
  -l {info,warn,fail}, --level {info,warn,fail}
                        minimum output level (default: info)
  -L, --list-policies   list all the official, built-in policies. Combine with -v to view policy change logs
  -M custom_policy.txt, --make-policy custom_policy.txt
                        creates a policy based on the target server (i.e.: the target server has the ideal
                        configuration that other servers should adhere to), and stores it in the file path specified
  -m, --manual          print the man page (Docker, PyPI, Snap, and Windows builds only)
  -n, --no-colors       disable colors (automatic when the NO_COLOR environment variable is set)
  -P "Built-In Policy Name" / custom_policy.txt, --policy "Built-In Policy Name" / custom_policy.txt
                        run a policy test using the specified policy (use -L to see built-in policies, or specify
                        filesystem path to custom policy created by -M)
  -p N, --port N        the TCP port to connect to (or to listen on when -c is used)
  -T targets.txt, --targets targets.txt
                        a file containing a list of target hosts (one per line, format HOST[:PORT]). Use -p/--port
                        to set the default port for all hosts. Use --threads to control concurrent scans
  -t N, --timeout N     timeout (in seconds) for connection and reading (default: 5)
  -v, --verbose         enable verbose output
  --conn-rate-test N[:max_rate]
                        perform a connection rate test (useful for collecting metrics related to susceptibility of
                        the DHEat vuln). Testing is conducted with N concurrent sockets with an optional maximum
                        rate of connections per second
  --dheat N[:kex[:e_len]]
                        continuously perform the DHEat DoS attack (CVE-2002-20001) against the target using N
                        concurrent sockets. Optionally, a specific key exchange algorithm can be specified instead
                        of allowing it to be automatically chosen. Additionally, a small length of the fake e value
                        sent to the server can be chosen for a more efficient attack (such as 4).
  --lookup alg1[,alg2,...]
                        looks up an algorithm(s) without connecting to a server.
  --skip-rate-test      skip the connection rate test during standard audits (used to safely infer whether the DHEat
                        attack is viable)
  --threads N           number of threads to use when scanning multiple targets (-T/--targets) (default: 32)
  • if both IPv4 and IPv6 are used, order of precedence can be set by using either -46 or -64.
  • batch flag -b will output sections without header and without empty lines (implies verbose flag).
  • verbose flag -v will prefix each line with section type and algorithm name.
  • an exit code of 0 is returned when all algorithms are considered secure (for a standard audit), or when a policy check passes (for a policy audit).

Basic server auditing:

ssh-audit localhost
ssh-audit 127.0.0.1
ssh-audit 127.0.0.1:222
ssh-audit ::1
ssh-audit [::1]:222

To run a standard audit against many servers (place targets into servers.txt, one on each line in the format of HOST[:PORT]):

ssh-audit -T servers.txt

To audit a client configuration (listens on port 2222 by default; connect using ssh -p 2222 anything@localhost):

ssh-audit -c

To audit a client configuration, with a listener on port 4567:

ssh-audit -c -p 4567

To list all official built-in policies (hint: use resulting policy names with -P/--policy):

ssh-audit -L

To run a policy audit against a server:

ssh-audit -P ["policy name" | path/to/server_policy.txt] targetserver

To run a policy audit against a client:

ssh-audit -c -P ["policy name" | path/to/client_policy.txt]

To run a policy audit against many servers:

ssh-audit -T servers.txt -P ["policy name" | path/to/server_policy.txt]

To create a policy based on a target server (which can be manually edited):

ssh-audit -M new_policy.txt targetserver

To run the DHEat CPU exhaustion DoS attack (CVE-2002-20001) against a target using 10 concurrent sockets:

ssh-audit --dheat=10 targetserver

To run the DHEat attack using the diffie-hellman-group-exchange-sha256 key exchange algorithm:

ssh-audit --dheat=10:diffie-hellman-group-exchange-sha256 targetserver

To run the DHEat attack using the diffie-hellman-group-exchange-sha256 key exchange algorithm along with very small but non-standard packet lengths (this may result in the same CPU exhaustion, but with many less bytes per second being sent):

ssh-audit --dheat=10:diffie-hellman-group-exchange-sha256:4 targetserver

Screenshots

Server Standard Audit Example

Below is a screen shot of the standard server-auditing output when connecting to an unhardened OpenSSH v5.3 service: screenshot

Server Policy Audit Example

Below is a screen shot of the policy auditing output when connecting to an un-hardened Ubuntu Server 20.04 machine (hint: use -L/--list-policies to see names of built-in policies to use with -P/--policy): screenshot

After applying the steps in the hardening guide (see below), the output changes to the following: screenshot

Client Standard Audit Example

Below is a screen shot of the client-auditing output when an unhardened OpenSSH v7.2 client connects: client_screenshot

Hardening Guides

Guides to harden server & client configuration can be found here: https://www.ssh-audit.com/hardening_guides.html

Pre-Built Packages

Pre-built packages are available for Windows (see the Releases page), PyPI, Snap, and Docker:

To install from PyPI:

$ pip3 install ssh-audit

To install the Snap package:

$ snap install ssh-audit

To install from Dockerhub:

$ docker pull positronsecurity/ssh-audit

(Then run with: docker run -it --rm -p 2222:2222 positronsecurity/ssh-audit 10.1.1.1)

The status of various other platform packages can be found below (via Repology):

Packaging status

Web Front-End

For convenience, a web front-end on top of the command-line tool is available at https://www.ssh-audit.com/.

ChangeLog

v3.4.0-dev

v3.3.0 (2024-10-15)

  • Added Python 3.13 support.
  • Added built-in policies for Ubuntu 24.04 LTS server & client, OpenSSH 9.8, and OpenSSH 9.9.
  • Added IPv6 support for DHEat and connection rate tests.
  • Added TCP port information to JSON policy scan results; credit Fabian Malte Kopp.
  • Added LANcom LCOS server recognition and Ed448 key extraction; credit Daniel Lenski.
  • Now reports ECDSA and DSS fingerprints when in verbose mode; partial credit Daniel Lenski.
  • Removed CVE information based on server/client version numbers, as this was wildly inaccurate (see this thread for the full discussion, as well as the results of the community vote on this matter).
  • Fixed crash when running with -P and -T options simultaneously.
  • Fixed host key tests from only reporting a key type at most once despite multiple hosts supporting it; credit Daniel Lenski.
  • Fixed DHEat connection rate testing on MacOS X and BSD platforms; credit Drew Noel and Michael Osipov.
  • Fixed invalid JSON output when a socket error occurs while performing a client audit.
  • Fixed --conn-rate-test feature on Windows.
  • When scanning multiple targets (using -T/--targets), the -p/--port option will now be used as the default port (set to 22 if -p/--port is not given). Hosts specified in the file can override this default with an explicit port number (i.e.: "host1:1234"). For example, when using -T targets.txt -p 222, all hosts in targets.txt that do not explicitly include a port number will default to 222; when using -T targets.txt (without -p), all hosts will use a default of 22.
  • Updated built-in server & client policies for Amazon Linux 2023, Debian 12, Rocky Linux 9, and Ubuntu 22.04 to improve host key efficiency and cipher resistance to quantum attacks.
  • Added 1 new cipher: grasshopper-ctr128.
  • Added 2 new key exchanges: mlkem768x25519-sha256, sntrup761x25519-sha512.

v3.2.0 (2024-04-22)

  • Added implementation of the DHEat denial-of-service attack (see --dheat option; CVE-2002-20001).
  • Expanded filter of CBC ciphers to flag for the Terrapin vulnerability. It now includes more rarely found ciphers.
  • Fixed parsing of ecdsa-sha2-nistp* CA signatures on host keys. Additionally, they are now flagged as potentially back-doored, just as standard host keys are.
  • Gracefully handle rare exceptions (i.e.: crashes) while performing GEX tests.
  • The built-in man page (-m, --manual) is now available on Docker, PyPI, and Snap builds, in addition to the Windows build.
  • Snap builds are now architecture-independent.
  • Changed Docker base image from python:3-slim to python:3-alpine, resulting in a 59% reduction in image size; credit Daniel Thamdrup.
  • Added built-in policies for Amazon Linux 2023, Debian 12, OpenSSH 9.7, and Rocky Linux 9.
  • Built-in policies now include a change log (use -L -v to view them).
  • Custom policies now support the allow_algorithm_subset_and_reordering directive to allow targets to pass with a subset and/or re-ordered list of host keys, kex, ciphers, and MACs. This allows for the creation of a baseline policy where targets can optionally implement stricter controls; partial credit yannik1015.
  • Custom policies now support the allow_larger_keys directive to allow targets to pass with larger host keys, CA keys, and Diffie-Hellman keys. This allows for the creation of a baseline policy where targets can optionally implement stricter controls; partial credit Damian Szuberski.
  • Color output is disabled if the NO_COLOR environment variable is set (see https://no-color.org/).
  • Added 1 new key exchange algorithm: gss-nistp384-sha384-*.
  • Added 1 new cipher: [email protected].

v3.1.0 (2023-12-20)

  • Added test for the Terrapin message prefix truncation vulnerability (CVE-2023-48795).
  • Dropped support for Python 3.7 (EOL was reached in June 2023).
  • Added Python 3.12 support.
  • In server policies, reduced expected DH modulus sizes from 4096 to 3072 to match the online hardening guides (note that 3072-bit moduli provide the equivalent of 128-bit symmetric security).
  • In Ubuntu 22.04 client policy, moved host key types [email protected] and ssh-ed25519 to the end of all certificate types.
  • Updated Ubuntu Server & Client policies for 20.04 and 22.04 to account for key exchange list changes due to Terrapin vulnerability patches.
  • Re-organized option host key types for OpenSSH 9.2 server policy to correspond with updated Debian 12 hardening guide.
  • Added built-in policies for OpenSSH 9.5 and 9.6.
  • Added an additional_notes field to the JSON output.

v3.0.0 (2023-09-07)

  • Results from concurrent scans against multiple hosts are no longer improperly combined; bug discovered by Adam Russell.
  • Hostname resolution failure no longer causes scans against multiple hosts to terminate unexpectedly; credit Dani Cuesta.
  • Algorithm recommendations resulting from warnings are now printed in yellow instead of red; credit Adam Russell.
  • Added failure, warning, and info notes to JSON output (note that this results in a breaking change to the banner protocol, "enc", and "mac" fields); credit Bareq Al-Azzawi.
  • Docker Makefile now creates multi-arch builds for amd64, arm64, and armv7; credit Sebastian Cohnen.
  • Fixed crash during GEX tests.
  • Refined GEX testing against OpenSSH servers: when the fallback mechanism is suspected of being triggered, perform an additional test to obtain more accurate results.
  • The color of all notes will be printed in green when the related algorithm is rated good.
  • Prioritized host key certificate algorithms for Ubuntu 22.04 LTS client policy.
  • Marked all NIST K-, B-, and T-curves as unproven since they are so rarely used.
  • Added built-in policy for OpenSSH 9.4.
  • Added 12 new host keys: ecdsa-sha2-curve25519, ecdsa-sha2-nistb233, ecdsa-sha2-nistb409, ecdsa-sha2-nistk163, ecdsa-sha2-nistk233, ecdsa-sha2-nistk283, ecdsa-sha2-nistk409, ecdsa-sha2-nistp224, ecdsa-sha2-nistp192, ecdsa-sha2-nistt571, ssh-dsa, x509v3-sign-rsa-sha256.
  • Added 15 new key exchanges: [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], kexAlgoDH14SHA1, kexAlgoDH1SHA1, kexAlgoECDH256, kexAlgoECDH384, kexAlgoECDH521, sm2kep-sha2-nistp256, [email protected], [email protected].
  • Added 8 new ciphers: [email protected], cast128-12-cbc, cast128-12-cfb, cast128-12-ecb, cast128-12-ofb, des-cfb, des-ecb, des-ofb.
  • Added 14 new MACs: cbcmac-3des, cbcmac-aes, cbcmac-blowfish, cbcmac-des, cbcmac-rijndael, cbcmac-twofish, hmac-sha256-96, md5, md5-8, ripemd160, ripemd160-8, sha1, sha1-8, umac-128.

v2.9.0 (2023-04-29)

v2.5.0 (2021-08-26)

  • Fixed crash when running host key tests.
  • Handles server connection failures more gracefully.
  • Now prints JSON with indents when -jj is used (useful for debugging).
  • Added MD5 fingerprints to verbose output.
  • Added -d/--debug option for getting debugging output; credit Adam Russell.
  • Updated JSON output to include MD5 fingerprints. Note that this results in a breaking change in the 'fingerprints' dictionary format.
  • Updated OpenSSH 8.1 (and earlier) policies to include rsa-sha2-512 and rsa-sha2-256.
  • Added OpenSSH v8.6 & v8.7 policies.
  • Added 3 new key exchanges: gss-gex-sha1-eipGX3TCiQSrx573bT1o1Q==, gss-group1-sha1-eipGX3TCiQSrx573bT1o1Q==, and gss-group14-sha1-eipGX3TCiQSrx573bT1o1Q==.
  • Added 3 new MACs: hmac-ripemd160-96, AEAD_AES_128_GCM, and AEAD_AES_256_GCM.

v2.4.0 (2021-02-23)

  • Added multi-threaded scanning support.
  • Added built-in Windows manual page (see -m/--manual); credit Adam Russell.
  • Added version check for OpenSSH user enumeration (CVE-2018-15473).
  • Added deprecation note to host key types based on SHA-1.
  • Added extra warnings for SSHv1.
  • Added built-in hardened OpenSSH v8.5 policy.
  • Upgraded warnings to failures for host key types based on SHA-1.
  • Fixed crash when receiving unexpected response during host key test.
  • Fixed hang against older Cisco devices during host key test & gex test.
  • Fixed improper termination while scanning multiple targets when one target returns an error.
  • Dropped support for Python 3.5 (which reached EOL in Sept. 2020).
  • Added 1 new key exchange: [email protected].

v2.3.1 (2020-10-28)

  • Now parses public key sizes for [email protected] and [email protected] host key types.
  • Flag [email protected] as a failure due to SHA-1 hash.
  • Fixed bug in recommendation output which suppressed some algorithms inappropriately.
  • Built-in policies now include CA key requirements (if certificates are in use).
  • Lookup function (--lookup) now performs case-insensitive lookups of similar algorithms; credit Adam Russell.
  • Migrated pre-made policies from external files to internal database.
  • Split single 3,500 line script into many files (by class).
  • Added setup.py support; credit Ganden Schaffner.
  • Added 1 new cipher: [email protected].

v2.3.0 (2020-09-27)

  • Added new policy auditing functionality to test adherence to a hardening guide/standard configuration (see -L/--list-policies, -M/--make-policy and -P/--policy). For an in-depth tutorial, see https://www.positronsecurity.com/blog/2020-09-27-ssh-policy-configuration-checks-with-ssh-audit/.
  • Created new man page (see ssh-audit.1 file).
  • 1024-bit moduli upgraded from warnings to failures.
  • Many Python 2 code clean-ups, testing framework improvements, pylint & flake8 fixes, and mypy type comments; credit Jürgen Gmach.
  • Added feature to look up algorithms in internal database (see --lookup); credit Adam Russell.
  • Suppress recommendation of token host key types.
  • Added check for use-after-free vulnerability in PuTTY v0.73.
  • Added 11 new host key types: ssh-rsa1, [email protected], ssh-gost2001, ssh-gost2012-256, ssh-gost2012-512, spki-sign-rsa, ssh-ed448, x509v3-ecdsa-sha2-nistp256, x509v3-ecdsa-sha2-nistp384, x509v3-ecdsa-sha2-nistp521, x509v3-rsa2048-sha256.
  • Added 8 new key exchanges: diffie-hellman-group1-sha256, kexAlgoCurve25519SHA256, Curve25519SHA256, gss-group14-sha256-, gss-group15-sha512-, gss-group16-sha512-, gss-nistp256-sha256-, gss-curve25519-sha256-.
  • Added 5 new ciphers: blowfish, AEAD_AES_128_GCM, AEAD_AES_256_GCM, [email protected], [email protected].
  • Added 3 new MACs: [email protected], hmac-sha3-224, [email protected].

v2.2.0 (2020-03-11)

v2.1.1 (2019-11-26)

  • Added 2 new host key types: [email protected], [email protected].
  • Added 2 new ciphers: des, 3des.
  • Added 3 new PuTTY vulnerabilities.
  • During client testing, client IP address is now listed in output.

v2.1.0 (2019-11-14)

  • Added client software auditing functionality (see -c / --client-audit option).
  • Added JSON output option (see -j / --json option; credit Andreas Jaggi).
  • Fixed crash while scanning Solaris Sun_SSH.
  • Added 9 new key exchanges: gss-group1-sha1-toWM5Slw5Ew8Mqkay+al2g==, gss-gex-sha1-toWM5Slw5Ew8Mqkay+al2g==, gss-group14-sha1-, gss-group14-sha1-toWM5Slw5Ew8Mqkay+al2g==, gss-group14-sha256-toWM5Slw5Ew8Mqkay+al2g==, gss-group15-sha512-toWM5Slw5Ew8Mqkay+al2g==, diffie-hellman-group15-sha256, ecdh-sha2-1.3.132.0.10, curve448-sha512.
  • Added 1 new host key type: ecdsa-sha2-1.3.132.0.10.
  • Added 4 new ciphers: idea-cbc, serpent128-cbc, serpent192-cbc, serpent256-cbc.
  • Added 6 new MACs: [email protected], [email protected], hmac-ripemd, [email protected], [email protected], [email protected].

v2.0.0 (2019-08-29)

  • Forked from https://github.com/arthepsy/ssh-audit (development was stalled, and developer went MIA).
  • Added RSA host key length test.
  • Added RSA certificate key length test.
  • Added Diffie-Hellman modulus size test.
  • Now outputs host key fingerprints for RSA and ED25519.
  • Added 5 new key exchanges: [email protected], [email protected], [email protected], diffie-hellman-group16-sha256, diffie-hellman-group17-sha512.
  • Added 3 new encryption algorithms: des-cbc-ssh1, blowfish-ctr, twofish-ctr.
  • Added 10 new MACs: hmac-sha2-56, hmac-sha2-224, hmac-sha2-384, hmac-sha3-256, hmac-sha3-384, hmac-sha3-512, hmac-sha256, [email protected], hmac-sha512, [email protected].
  • Added command line argument (-t / --timeout) for connection & reading timeouts.
  • Updated CVEs for libssh & Dropbear.

v1.7.0 (2016-10-26)

  • implement options to allow specify IPv4/IPv6 usage and order of precedence
  • implement option to specify remote port (old behavior kept for compatibility)
  • add colors support for Microsoft Windows via optional colorama dependency
  • fix encoding and decoding issues, add tests, do not crash on encoding errors
  • use mypy-lang for static type checking and verify all code

v1.6.0 (2016-10-14)

  • implement algorithm recommendations section (based on recognized software)
  • implement full libssh support (version history, algorithms, security, etc)
  • fix SSH-1.99 banner recognition and version comparison functionality
  • do not output empty algorithms (happens for misconfigured servers)
  • make consistent output for Python 3.x versions
  • add a lot more tests (conf, banner, software, SSH1/SSH2, output, etc)
  • use Travis CI to test for multiple Python versions (2.6-3.5, pypy, pypy3)

v1.5.0 (2016-09-20)

  • create security section for related security information
  • match and output assigned CVE list and security issues for Dropbear SSH
  • implement full SSH1 support with fingerprint information
  • automatically fallback to SSH1 on protocol mismatch
  • add new options to force SSH1 or SSH2 (both allowed by default)
  • parse banner information and convert it to specific software and OS version
  • do not use padding in batch mode
  • several fixes (Cisco sshd, rare hangs, error handling, etc)

v1.0.20160902

  • implement batch output option
  • implement minimum output level option
  • fix compatibility with Python 2.6

v1.0.20160812

  • implement SSH version compatibility feature
  • fix wrong mac algorithm warning
  • fix Dropbear SSH version typo
  • parse pre-banner header
  • better errors handling

v1.0.20160803

  • use OpenSSH 7.3 banner
  • add new key-exchange algorithms

v1.0.20160207

  • use OpenSSH 7.2 banner
  • additional warnings for OpenSSH 7.2
  • fix OpenSSH 7.0 failure messages
  • add rijndael-cbc failure message from OpenSSH 6.7

v1.0.20160105

  • multiple additional warnings
  • support for none algorithm
  • better compression handling
  • ensure reading enough data (fixes few Linux SSH)

v1.0.20151230

  • Dropbear SSH support

v1.0.20151223

  • initial version

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SSH server & client security auditing (banner, key exchange, encryption, mac, compression, compatibility, security, etc)

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