Ansible-pylibssh: accepts a changed ssh host key when host_key_auto_add is enabled
Summary
| CVE | CVE-2026-126641 |
|---|---|
| State | PUBLISHED |
| Assigner | redhat |
| Source Priority | CVE Program / NVD first with legacy fallback |
| Published | 2026-11-12 11:17:11 UTC |
| Updated | 2026-11-12 11:17:11 UTC |
| Description | A host key verification flaw was found in ansible-pylibssh and in the ansible.netcommon libssh connection plugin. When trust-on-first-use is enabled (host_key_auto_add on the libssh connection plugin, or AutoAddPolicy in ansible-pylibssh), a host that is already present in known_hosts but now presents a different key is accepted without warning. The pylibssh Session.verify_knownhost() method passes the SSH_KNOWN_HOSTS_CHANGED and SSH_KNOWN_HOSTS_OTHER states to the same missing_host_key() policy hook used for unknown hosts, and the bundled AutoAddPolicy/RejectPolicy classes (as well as ansible.netcommon's MyAddPolicy, which is modeled on paramiko's AutoAddPolicy) therefore add the changed key and continue the connection rather than aborting as paramiko's BadHostKeyException path would. As a result the controller authenticates to the substitute host, runs the play there, and appends the new key to known_hosts, which can disclose connection credentials to an attacker performing a machine-in-the-middle attack. Default configurations (host_key_checking enabled, host_key_auto_add unset) are not affected; non-interactive runs fail closed. |
Risk And Classification
Primary CVSS: v3.1 6.5 MEDIUM from [email protected]
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:N
Problem Types: CWE-322 | CWE-322 Key Exchange without Entity Authentication
| Version | Source | Type | Score | Severity | Vector |
|---|---|---|---|---|---|
| 3.1 | [email protected] | Primary | 6.5 | MEDIUM | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:N |
| 3.1 | CNA | CVSS | 6.5 | MEDIUM | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:N |
CVSS v3.1 Breakdown
Attack Vector
NetworkAttack Complexity
HighPrivileges Required
NoneUser Interaction
NoneScope
UnchangedConfidentiality
HighIntegrity
LowAvailability
NoneCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:N
Vendor Declared Affected Products
| Source | Vendor | Product | Version | Platforms |
|---|---|---|---|---|
| CNA | Red Hat | Red Hat Ansible Automation Platform 2 | Not specified | Not specified |
| CNA | Red Hat | Red Hat Ansible Automation Platform 2 | Not specified | Not specified |
| CNA | Red Hat | Red Hat Ansible Automation Platform 2 | Not specified | Not specified |
| CNA | Red Hat | Red Hat Ansible Automation Platform 2 | Not specified | Not specified |
| CNA | Red Hat | Red Hat Ansible Automation Platform 2 | Not specified | Not specified |
| CNA | Red Hat | Red Hat Ansible Automation Platform 2 | Not specified | Not specified |
References
| Reference | Source | Link | Tags |
|---|---|---|---|
| access.redhat.com/security/cve/CVE-2026-126641 | [email protected] | access.redhat.com | |
| bugzilla.redhat.com/show_bug.cgi | [email protected] | bugzilla.redhat.com | |
| CVE Program record | CVE.ORG | www.cve.org | canonical |
| NVD vulnerability detail | NVD | nvd.nist.gov | canonical, analysis |
Vendor Comments And Credit
Discovery Credit
CNA: Red Hat would like to thank Satriyo Utomo (aleens-labs) for reporting this issue. (en)
Additional Advisory Data
| Source | Time | Event |
|---|---|---|
| CNA | 2026-11-11T14:10:25.855Z | Reported to Red Hat. |
| CNA | 2026-11-11T14:19:28.279Z | Made public. |
Workarounds
CNA: 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.
There are currently no legacy QID mappings associated with this CVE.