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Fencer Vulns
medium 6.5

CVE-2023-25136 json

OpenSSH server (sshd) 9.1 introduced a double-free vulnerability during options.kex_algorithms handling.

published 2023-02-03 3 y ago modified 2026-10-14 25 d ago also EUVD-2023-29115 , JLSEC-2026-66

cvss
6.5
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
89.8%
EPSS 89.8% chance of exploitation in 30 days, percentile 99.7%
public exploits
0
none known

Summary

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."

Patch / fix

  • julia OpenSSH_jll 9.1.0+0
  • Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP V3.1.5
  • Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP V3.1.5
  • Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP V3.1.5
  • openssh Debian 14, Debian 13, Debian 12 1:9.2p1-1

debian advisories DEBIAN-CVE-2023-25136

  • openssh RHEL 9 8.7p1-29.el9_2
  • openssh-keycat RHEL 9 8.7p1-29.el9_2
  • openssh-server RHEL 9 8.7p1-29.el9_2
  • openssh-askpass RHEL 9 8.7p1-29.el9_2
  • openssh-clients RHEL 9 8.7p1-29.el9_2
  • pam_ssh_agent_auth RHEL 9 0.10.4-5.29.el9_2

red hat advisories RHSA-2023:2645

  • openssh AlmaLinux 9 8.7p1-29.el9_2
  • openssh-keycat AlmaLinux 9 8.7p1-29.el9_2
  • openssh-server AlmaLinux 9 8.7p1-29.el9_2
  • openssh-askpass AlmaLinux 9 8.7p1-29.el9_2
  • openssh-clients AlmaLinux 9 8.7p1-29.el9_2
  • pam_ssh_agent_auth AlmaLinux 9 0.10.4-5.29.el9_2

almalinux advisories ALSA-2023:2645

  • openssh Arch Linux 9.2p1-1

arch linux advisories AVG-2832

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2023-25136 updated cvss 6.5

openssh: the functions order_hostkeyalgs() and list_hostkey_types() leads to double-free vulnerability

  • Red Hat Enterprise Linux AppStream (v. 9) openssh-askpass 8.7p1-29.el9_2, pam_ssh_agent_auth 0.10.4-5.29.el9_2 Red Hat Enterprise Linux BaseOS (v. 9) openssh 8.7p1-29.el9_2, openssh-keycat 8.7p1-29.el9_2, openssh-server 8.7p1-29.el9_2, openssh-clients 8.7p1-29.el9_2
    fixed: vendor fix RHSA-2023:2645
  • Red Hat Enterprise Linux 6 openssh, openssh-ldap, openssh-server, openssh-askpass, openssh-clients, pam_ssh_agent_auth Red Hat Enterprise Linux 7 openssh, openssh-cavs, openssh-ldap, openssh-keycat, openssh-server, openssh-askpass, +3 more Red Hat Enterprise Linux 8 openssh, openssh-cavs, openssh-ldap, openssh-keycat, openssh-server, openssh-askpass, +2 more
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

cisa ICSA-23-348-10 updated cvss 6.5

Siemens SIMATIC S7-1500

  • Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0) >= 3.1.0, < 3.1.5 Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AC0) >= 3.1.0, < 3.1.5 Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AB0) >= 3.1.0, < 3.1.5 Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AC0) >= 3.1.0, < 3.1.5 Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP (6AG1518-4AX00-4AC0) >= 3.1.0, < 3.1.5
    affected: fixed in V3.1.5, mitigation support.industry.siemens.com

Facts from CISA's republication of the vendor's own advisory (CSAF); the linked advisory is the authoritative source. CISA notification · csaf

CISA SSVC

Exploitation
Proof of concept is public
Automatable
no
Technical impact
partial
Assessed
2 y ago

Exploit prediction

89.79% chance of exploitation in the next 30 days, higher than 99.7% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • openwall.com https://www.openwall.com/lists/oss-security/2023/02/02/2 referenced PoC, tagged "exploit" by a source, unverified
  • bugzilla.mindrot.org https://bugzilla.mindrot.org/show_bug.cgi?id=3522 referenced PoC, tagged "exploit" by a source, unverified
  • jfrog.com https://jfrog.com/blog/openssh-pre-auth-double-free-cve-2023-25136-writeup-and-proof-of-concept/ referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
NVD 3.1 6.5 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:H
OSV 3.1 6.5 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:H

Affected packages

ecosystem package affected fixed in
julia OpenSSH_jll
>=8.9.0+0, <9.1.0+0
9.1.0+0

Affected products

  • Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP
  • Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP
  • Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP

Classification

Weakness

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.