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Public proof of conceptFix available

CVE-2025-26466

A public proof of concept exists; no exploitation attested.

  • Published2025-02-28
  • WeaknessCWE-770

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

Description

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.

Timeline

dates in UTC
  1. 2025-02-2822:15CVE publishedNVD

Observed activity

isMalicious corpus · updated 2026-10-23 18:48 UTC
Indicators tagged with this CVE, per day0 indicators over 7 days
Block these indicators
  • Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2025-26466?format=txt
  • CSV export: https://api.ismalicious.com/edl/cve/CVE-2025-26466?format=csv
  • TAXII collection of exploited CVEs
  • The EDL and CSV take an API key on the Pro plan.

Versions per branch

NVD
OpenSSH
BranchAffectedFixed in
9.5= 9.5no fix published
9.6= 9.6no fix published
9.7= 9.7no fix published
9.8= 9.8no fix published
9.9= 9.9no fix published
Debian debian linux
BranchAffectedFixed in
11.0= 11.0no fix published
12.0= 12.0no fix published
13.0= 13.0no fix published
Canonical ubuntu linux
BranchAffectedFixed in
24.4= 24.04no fix published
24.10= 24.10no fix published

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Distribution builds and vendor advisories

Packages from OSV.dev and products from the vendors' CSAF advisories.

version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.

Vendor advisories

  • CVE-2025-26466 Red Hat Product Security178 products fixed

    openssh: Denial-of-service in OpenSSH

  • RHSA-2025:6993 Red Hat Product Security89 products fixed

    Red Hat Security Advisory: openssh security update

  • RHBA-2025:6305 Red Hat Product Security89 products fixed

    Red Hat Bug Fix Advisory: openssh bug fix and enhancement update

  • ICSA-23-348-10 CISA5 known affected

    Siemens SIMATIC S7-1500

    SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0) · SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AC0) · SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AB0) · +2 more

  • SSA-398330 Siemens ProductCERT5 known affected

    SSA-398330: Vulnerabilities in the additional GNU/Linux subsystem of the SIMATIC S7-1500 CPU 1518(F)-4 PN/DP MFP >= V3.1.0 and < V3.1.5

    SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0) >= V3.1.0 < V3.1.5 · SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AC0) >= V3.1.0 < V3.1.5 · SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AB0) >= V3.1.0 < V3.1.5 · +2 more

Full record on NVD

Fix

  1. Vendor fix Red Hat Product Security RHSA-2025:6993 · 89 productsFor details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258
  2. Vendor fix CISA ICSA-23-348-10 · 5 productsUpdate to V3.1.5 or later version
  3. Vendor fix Siemens ProductCERT SSA-398330 · 1 productUpdate to V3.1.5 or later version
  4. Workaround from the vendor Red Hat Product Security RHSA-2025:6993 · 89 productsThis issue can be mitigated by setting the following three different options in the sshd configuration file located at: /etc/ssh/sshd_config MaxStartups: Set to a reasonable value, this option controls the maximum number of concurrent unauthenticated connections the SSH server accepts; PerSourceP…
  5. Mitigation from the vendor CISA ICSA-23-348-10 · 5 productsOnly build and run applications from trusted sources.

Detection

read 2026-10-23 19:24 UTC
Nuclei template
none so far
ProjectDiscovery
Exploit-DB
no entry
Exploit-DB
Proof-of-concept repositories
5 repositories, unverifiedrxerium/CVE-2025-26466mrowkoob/CVE-2025-26466-msftpirate/CVE-2025-26466acidboonrs/cve-2025-26466-openssh-pocK0n9-log/cve-2025-26466-canvas
PoC-in-GitHub

Sources

  • CISA-ADPSSVC decisionpoc2025-03-04
  • OpenCVESSVC decisionpoc—
  • CNACVSS 3.15.9read 2026-10-23
  • NVDCVSS 3.15.9read 2026-10-23
  • CNAweakness (CWE)CWE-770read 2026-10-23
  • NVDweakness (CWE)CWE-770read 2026-10-23
  • FIRST EPSSEPSS score40.7 %read 2026-10-23
  • PoC-in-GitHubproof of concept5read 2026-10-23

Technical details

CVSS v3 Vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
Published
2025-02-28
Last Modified
2026-10-21
NVD status
Modified

Frequently asked questions

What is CVE-2025-26466?

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.

Is CVE-2025-26466 actively exploited?

A proof-of-concept exploit exists for CVE-2025-26466, but active exploitation has not been confirmed at this time.

What is the CVSS score for CVE-2025-26466?

CVE-2025-26466 has a CVSS v3 base score of 5.9 (MEDIUM severity), with vector string CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H.

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