Full Report
A vulnerability has been discovered in OpenSSH which could allow for authentication bypass. OpenSSH (Open Secdure Shell) is an open-source suite of secure networking utilities based on the SSH protocol. It provides encrypted communication sessions over unsecured networks in a client-server architecture, primarily used for remote login and secure file transfers. Successful exploitation of the vulnerability could provide an attacker with root access to all the servers an organization has, if the vulnerable protocol runs on them.
Analysis Summary
# Vulnerability: OpenSSH Authentication Bypass via Certificate Principal Mishandling
## CVE Details
- **CVE ID:** CVE-2026-35414
- **CVSS Score:** Not explicitly listed, but impact is rated as **High** (potential for full root access).
- **CWE:** CWE-287 (Improper Authentication) / CWE-20 (Improper Input Validation)
## Affected Systems
- **Products:** OpenSSH (Open Secure Shell)
- **Versions:** All versions prior to **10.3**
- **Configurations:** Systems using SSH Certificate Authority (CA) authentication where the `authorized_keys` file utilizes the `principals` option. The flaw is triggered when a trusted CA issues a certificate containing a comma (`,`) character in the principal name.
## Vulnerability Description
The vulnerability stems from the way OpenSSH mishandles the `authorized_keys` "principals" option. In specific scenarios where a Certificate Authority includes a comma within a certificate's principal name, OpenSSH fails to parse the string correctly. Because commas are often used as delimiters in configuration files, this leading to an access control bypass. An attacker possessing a valid certificate from a trusted CA can exploit this parsing error to authenticate as a different user, including **root**, effectively bypassing intended authorization restrictions.
## Exploitation
- **Status:** PoC available. Cyera has successfully demonstrated exploitation using a test certificate and test server.
- **Complexity:** Medium (Requires a valid certificate from a trusted CA).
- **Attack Vector:** Network
## Impact
- **Confidentiality:** High (Full access to server data)
- **Integrity:** High (Ability to modify any file on the system as root)
- **Availability:** High (Ability to shut down or disrupt services)
## Remediation
### Patches
- Upgrade to **OpenSSH version 10.3** or later immediately.
### Workarounds
- **Principal Review:** Audit trusted Certificate Authorities to ensure they do not issue certificates containing comma characters in principal names.
- **Least Privilege:** Ensure that the SSH service is configured with the "Principle of Least Privilege" where possible, though this vulnerability specifically targets escalated (root) access.
## Detection
- **Indicators of Compromise:** Review authentication logs for successful root logins originating from unexpected certificates or certificates containing unusual characters (commas) in the identity field.
- **Detection Methods:**
- Perform automated vulnerability scans using SCAP-compliant tools to identify outdated OpenSSH versions.
- Conduct internal and external penetration testing to verify the robustness of SSH certificate configurations.
## References
- **CVE:** hxxps[://]cve[.]mitre[.]org/cgi-bin/cvename[.]cgi?name=CVE-2026-35414
- **Security Week:** hxxps[://]www[.]securityweek[.]com/openssh-flaw-allowing-full-root-shell-access-lurked-for-15-years/
- **CIS Advisory:** MS-ISAC ADVISORY NUMBER: 2026-040