CVE
Red Hat Ansible Automation Platform 2 host key check bypass in ansible-pylibssh
- Exploited
- No known exploitation
- Fix
- See vendor advisory
- Who is exposed
- Not reported
- Last modified
- Whether it needs action now or is a reference record, by fixed rules, with why. Last checked is when cve.now last re-read it.What do these mean? →
- Reference
- Last checked
- FIRST's estimate of the chance attackers exploit it in the next 30 days, updated daily.What do these mean? →
- 0.33% · 26th percentile
- A 0-100 score for how much a CVE matters across the industry: exploitation, exposure, how widely the software is used, severity and whether a fix exists.What do these mean? →
- 39/100 · provisional
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- None on Exploit-DB, Metasploit or GitHub
- Exploitation: none
- Automatable: no
- Technical impact: partial
Summary
The ansible-pylibssh library and the ansible.netcommon libssh connection plugin in Red Hat Ansible Automation Platform 2 accept a changed SSH host key without warning when trust-on-first-use (host_key_auto_add) is enabled. A remote attacker positioned as a machine-in-the-middle can, without logging in or any user action, get the controller to run plays on a substitute host and potentially disclose connection credentials.
Written by anthropic/claude-haiku-5.5 from the sources below. Verify against them.
Read the original 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.
cve.now Index
- Exploitation0/40No signal
- Exposure17/25No login or user action needed per the CVSS vector, reachable over the network without a login · Unknown: No advisory context yet
- Reach10/20Shipped in major Linux distributions
- Severity6.5/10CVSS 6.5
- No patch5/5No fixed version listed; see vendor advisory
What would change the score
- Would score about 84 if added to CISA KEV
- Would score about 79 if CISA's SSVC rates exploitation active
- Would score about 44 if advisories confirm default setups are exposed
Check your systems with an agent
Paste this into a coding or ops agent. It checks your systems read-only and reports a table per asset.
Check whether my systems are affected by CVE-2026-126641 (Ansible-pylibssh: accepts a changed ssh host key when host_key_auto_add is enabled), using the cve.now data below.
Rules: work read-only. Do not run exploit code, proof-of-concept scripts or scanners that send attack payloads, and do not change any configuration, package, image or deployment. Report findings only.
What cve.now has for CVE-2026-126641 (entry last updated 2026-11-13):
Affected:
- Red Hat Red Hat Ansible Automation Platform 2: version range not reported
- Red Hat Red Hat Ansible Automation Platform 2: version range not reported
- Red Hat Red Hat Ansible Automation Platform 2: version range not reported
- Red Hat Red Hat Ansible Automation Platform 2: version range not reported
- Red Hat Red Hat Ansible Automation Platform 2: version range not reported
- Red Hat Red Hat Ansible Automation Platform 2: version range not reported
Fixed versions: none listed yet.
Setup: unknown whether the bug needs a non-default feature or setting. Check the advisory.
CISA KEV: CVE-2026-126641 is not listed as of cve.now's last read.
This KEV status is for CVE-2026-126641 only. If you also check another CVE, look up its own KEV status; never assume it from this one.
How to check:
- Installed software: check what is actually running, not what a repo declares. Read the version from each host, container image and Kubernetes node (the binary's version output, the OS package database, image layers), and check whether the conditions above hold there. Distribution packages may carry a backported fix under an older version number; confirm against the distribution's own advisory.
Verify against the linked advisories before concluding, and cite the date you read each one:
- https://bugzilla.redhat.com/show_bug.cgi?id=2571719
- https://access.redhat.com/security/cve/CVE-2026-126641
- http://www.openwall.com/lists/oss-security/2026/11/12/6
Do not conclude an asset is unaffected unless you checked it and the evidence covers both its version and the conditions above. If you could not check something, mark it unknown and say what is missing.
Report a table with one row per asset and these columns: Asset | Version or build | Status (affected, fixed, not applicable, unknown) | Compensating controls | Exposure (internet-facing, internal, none) | Evidence | Next action.
Entry: https://cve.now/CVE-2026-126641
For follow-up questions, use the cve.now MCP server at https://mcp.cve.now/mcp (no authentication), for example execute with name cve.get and arguments {"id": "CVE-2026-126641"}.Timeline
- CVE published
- First seen by cve.now1 day
- CISA SSVC assessment
Exploitation: none · Automatable: no · Technical impact: partial
- Record last updated
Affected versions
- ansible-automation-platform-26/ee-supported-rhel9
Version range not reported
- ansible-automation-platform-27/ee-supported-rhel9
Version range not reported
- python3.11-ansible-pylibssh
Version range not reported
- python3.12-ansible-pylibssh
Version range not reported
- python3x-ansible-pylibssh
Version range not reported
- python-ansible-pylibssh
Version range not reported
Evidence 5
CVE record · 2
Establishes: The identifier and description.
- Record
- Record
Write-ups · 2
Establishes: Technical detail and context.
- Report
- Link
Other links · 1
- Link
Corrections
None so far.
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