CVE-2023-25136 — OpenSSH server (sshd) 9

OpenSSH server (sshd) 9.1 introduced a double-free vulnerability during options.kex_algorithms handling. This is fixed in OpenSSH 9.2. The double free can be leveraged, by an unauthenticated remote attacker in the default configuration, to jump to any location in the sshd address

01What is this vulnerability?

OpenSSH server (sshd) 9.1 introduced a double-free vulnerability during options.kex_algorithms handling. This is fixed in OpenSSH 9.2. The double free can be leveraged, by an unauthenticated remote attacker in the default configuration, to jump to any location in the sshd address space. One third-party report states "remote code execution is theoretically possible."

02Affected products

No structured affected-product list available — see references below for vendor advisories.

03Active exploitation status

Not currently listed on the CISA Known Exploited Vulnerabilities (KEV) catalog. EPSS is the best forward-looking signal — see the EPSS row above.

04Recommended remediation

• Patch to a fixed version listed in the vendor advisory (see references below).
• Mitigate with WAF rules, network egress filters, or feature flags where the patch is not yet available.
• Hunt historical logs for exploitation indicators — see Detection signatures below.

05Technical details

For the full vendor write-up, exploit chains, and reference implementations, see the references list in section 09.

06Detection signatures

Ask SARA in chat to draft a starting detection for this CVE in your stack of choice.

07Related CVEs

No directly-cited follow-up CVEs in the KB record for this advisory. The references list in section 09 carries the vendor cross-references.

08Timeline

• Published: 2023-02-03T06:15:09.350
• Last modified: 2026-10-14T23:17:15.010

09References

• www.openwall.com — http://www.openwall.com/lists/oss-security/2023/02/13/1
• www.openwall.com — http://www.openwall.com/lists/oss-security/2023/02/22/1
• www.openwall.com — http://www.openwall.com/lists/oss-security/2023/02/22/2
• www.openwall.com — http://www.openwall.com/lists/oss-security/2023/02/23/3
• www.openwall.com — http://www.openwall.com/lists/oss-security/2023/03/06/1
• www.openwall.com — http://www.openwall.com/lists/oss-security/2023/03/09/2
• bugzilla.mindrot.org — https://bugzilla.mindrot.org/show_bug.cgi?id=3522
• ftp.openbsd.org — https://ftp.openbsd.org/pub/OpenBSD/patches/7.2/common/017_sshd.patch.sig
• github.com — https://github.com/openssh/openssh-portable/commit/486c4dc3b83b4b67d663fb0fa62bc…
• jfrog.com — https://jfrog.com/blog/openssh-pre-auth-double-free-cve-2023-25136-writeup-and-p…