CVE-2023-25136

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.

Weakness

The product calls free() twice on the same memory address, potentially leading to modification of unexpected memory locations.

Affected Software

Potential Mitigations

References

• 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://bugzilla.mindrot.org/show_bug.cgi?id=3522
• https://ftp.openbsd.org/pub/OpenBSD/patches/7.2/common/017_sshd.patch.sig
• 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://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/JGAUIXJ3TEKCRKVWFQ6GDAGQFTIIGQQP/
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/R7LKQDFZWKYHQ65TBSH2X2HJQ4V2THS3/
• https://news.ycombinator.com/item?id=34711565
• https://security.gentoo.org/glsa/202307-01
• https://security.netapp.com/advisory/ntap-20230309-0003/
• https://www.openwall.com/lists/oss-security/2023/02/02/2