# CVE-2026-126641: ansible-pylibssh host key verification bypass in SSH connection

Source: https://junglewise.ai/threats/cve-2026-126641-a-host-key-verification-flaw-was-found-in-ansible-pylibssh-and  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-11-12. Updated: 2026-11-12  
License: CC BY 4.0 with a link back

CVE-2026-126641 · Severity: medium · CVSS 6.5 · Published 2026-11-12

Ansible's SSH connection libraries accept changed SSH host keys when trust-on-first-use mode is enabled, allowing attackers to intercept connections by presenting a different key. This enables man-in-the-middle attacks where credentials can be stolen and plays executed on the attacker's machine instead of the intended target. Default configurations are not affected; only deployments that explicitly enable host_key_auto_add or AutoAddPolicy are vulnerable.

Vendors: [Ansible](https://junglewise.ai/threats/vendors/ansible).

## Quick answers

**Is CVE-2026-126641 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-126641 being exploited in the wild.

**How severe is CVE-2026-126641?** Medium severity, with a CVSS score of 6.5, published 12 November 2026.

**Which products and versions are affected?** Ansible.Netcommon libssh connection plugin.

**Is there a fix for CVE-2026-126641?** No fixed version is recorded yet. Do not enable host_key_auto_add (ansible.netcommon libssh) or AutoAddPolicy (ansible-pylibssh). Keep host_key_checking enabled and pre-populate known_hosts with verified host keys so that a changed key causes the connection to fail closed.</anigation>
<parameter name="timeline">[
  {
    "kind": "disclosed",
    "at": "2026-11-12"
  }
] If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-126641 attacked?** It is attacked over the network.

**Am I affected by CVE-2026-126641?** Check whether you run Ansible-Pylibssh or Ansible.Netcommon at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix


Do not enable host_key_auto_add (ansible.netcommon libssh) or AutoAddPolicy (ansible-pylibssh). Keep host_key_checking enabled and pre-populate known_hosts with verified host keys so that a changed key causes the connection to fail closed.</anigation>
<parameter name="timeline">[
  {
    "kind": "disclosed",
    "at": "2026-11-12"
  }
]

## Technical details

The vulnerability exists in the pylibssh Session.verify_knownhost() method, which incorrectly routes SSH_KNOWN_HOSTS_CHANGED and SSH_KNOWN_HOSTS_OTHER states through the same missing_host_key() policy hook designed for unknown hosts. This causes AutoAddPolicy and MyAddPolicy classes to accept the changed key and continue the connection rather than abort, enabling a network-based man-in-the-middle attack. The attack requires the attacker to be positioned to intercept the connection and a prior known_hosts entry to exist for the target host.

## Affected products

- Ansible ansible-pylibssh
- Ansible ansible.netcommon libssh connection plugin

## References

- [https://access.redhat.com/downloads/content/package-browser/](https://access.redhat.com/downloads/content/package-browser/)
- [https://access.redhat.com/security/cve/CVE-2026-126641](https://access.redhat.com/security/cve/CVE-2026-126641)