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Fencer Vulns
medium 5.9

CVE-2025-26466 json

Openssh: denial-of-service in openssh

published 2025-02-28 20 mo ago modified 2026-11-05 3 d ago also EUVD-2025-5920

cvss
5.9
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
38.7%
EPSS 38.7% chance of exploitation in 30 days, percentile 98%
public exploits
0
none known

Summary

A flaw was found in the OpenSSH package. For each ping packet the SSH server receives, a pong packet is allocated in a memory buffer and stored in a queue of packages. It is only freed when the server/client key exchange has finished. A malicious client may keep sending such packages, leading to an uncontrolled increase in memory consumption on the server side. Consequently, the server may become unavailable, resulting in a denial of service attack.

Patch / fix

  • Red Hat Red Hat Enterprise Linux 10 0:9.9p1-7.el10_0
  • Red Hat Red Hat Enterprise Linux 9 0:8.7p1-45.el9
  • 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 1:9.9p2-1

debian advisories DEBIAN-CVE-2025-26466

  • openssh Ubuntu 24.04 LTS 1:9.6p1-3ubuntu13.8

ubuntu advisories UBUNTU-CVE-2025-26466

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • openssh RHEL 10.0 9.9p1-7.el10_0
  • openssh-keycat RHEL 10.0 9.9p1-7.el10_0
  • openssh-server RHEL 10.0 9.9p1-7.el10_0
  • openssh-askpass RHEL 10.0 9.9p1-7.el10_0
  • openssh-clients RHEL 10.0 9.9p1-7.el10_0
  • openssh-keysign RHEL 10.0 9.9p1-7.el10_0
  • openssh RHEL 9 8.7p1-45.el9
  • openssh-keycat RHEL 9 8.7p1-45.el9

red hat advisories RHBA-2025:6305RHSA-2025:6993

  • openssh Linux Micro 6.0 9.6p1-3.1
  • openssh Linux Micro 6.1 9.6p1-slfo.1.1_2.1
  • openssh SLE Module for Basesystem 15 SP6, openSUSE Leap 15.6 9.6p1-150600.6.15.2
  • openssh-askpass-gnome SLE Module for Desktop Applications 15 SP6, openSUSE Leap 15.6 9.6p1-150600.6.15.1

suse advisories SUSE-SU-2025:20160-1SUSE-SU-2025:20226-1SUSE-SU-2025:0585-1

  • openssh openSUSE Tumbleweed 9.9p2-1.1

opensuse advisories openSUSE-SU-2025:14820-1

  • openssh Alpine 3.19 9.6_p1-r2
  • openssh Alpine 3.20 9.7_p1-r5
  • openssh Alpine 3.24, Alpine 3.23, Alpine 3.22 +1 more 9.9_p2-r0

alpine advisories ALPINE-CVE-2025-26466

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • openssh Azure Linux 3.0 9.8p1-3

azure linux advisories AZL-56898

Azure Linux vulnerability data, Copyright (c) Microsoft Corporation, from https://github.com/microsoft/AzureLinuxVulnerabilityData via OSV, under the MIT licence; changed: normalised to fixed package versions per release. MIT

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-2025-26466 updated cvss 5.9

openssh: Denial-of-service in OpenSSH

  • Red Hat Enterprise Linux AppStream (v. 9) openssh-askpass 8.7p1-45.el9, pam_ssh_agent_auth 0.10.4-5.45.el9
    fixed: vendor fix RHSA-2025:6993
  • Red Hat Enterprise Linux AppStream (v. 10) openssh-askpass 9.9p1-7.el10_0, openssh-keysign 9.9p1-7.el10_0
    fixed: vendor fix RHBA-2025:6305
  • Red Hat Enterprise Linux BaseOS (v. 9) openssh 8.7p1-45.el9, openssh-keycat 8.7p1-45.el9, openssh-server 8.7p1-45.el9, openssh-clients 8.7p1-45.el9
    fixed: vendor fix RHSA-2025:6993
  • Red Hat Enterprise Linux BaseOS (v. 10) openssh 9.9p1-7.el10_0, openssh-keycat 9.9p1-7.el10_0, openssh-server 9.9p1-7.el10_0, openssh-clients 9.9p1-7.el10_0
    fixed: vendor fix RHBA-2025:6305
  • 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 Red Hat OpenShift Container Platform 4 openshift/ose-rhel-coreos-8, openshift/ose-rhel-coreos-9
    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 SSVC

Exploitation
Proof of concept is public
Automatable
no
Technical impact
partial
Assessed
20 mo ago

Exploit prediction

38.68% chance of exploitation in the next 30 days, higher than 98% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • qualys.com https://www.qualys.com/2025/02/18/openssh-mitm-dos.txt referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 3.1 5.9 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
NVD 3.1 5.9 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected products

  • Red Hat Red Hat Enterprise Linux 10
  • Red Hat Red Hat Enterprise Linux 9
  • Red Hat Red Hat Enterprise Linux 6
  • Red Hat Red Hat Enterprise Linux 7
  • Red Hat Red Hat Enterprise Linux 8
  • Red Hat Red Hat OpenShift Container Platform 4
  • 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
  • CWE-770 Allocation of Resources Without Limits or Throttling

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.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.