CVE-2026-12610: SSSD YubiKey Use-After-Free DoS Vulnerability

Technical summary

The vulnerability exists in SSSD's PAM responder module, which handles authentication requests. When processing YubiKey or smartcard authentication, a memory pointer is incorrectly handled after being freed, creating a use-after-free condition (CWE-825). This memory safety flaw allows an attacker with local system access to provide specially crafted smartcard or YubiKey data that causes the responder process to access invalid memory, resulting in a crash. The CVSS v3.1 score of 6.4 (MEDIUM) reflects high impact potential (confidentiality, integrity, availability) constrained by local access requirement and high attack complexity.

Business impact

Organizations relying on YubiKey or smartcard authentication via SSSD face disruption risk to their authentication infrastructure. A successful exploit crashes the PAM responder, preventing legitimate users from authenticating until the service is manually restarted. In environments where SSSD is the primary authentication mechanism for system access, this creates operational friction and potential support escalations. The denial-of-service impact is particularly concerning for critical systems where authentication failures cascade into broader service unavailability. Privilege escalation potential, though difficult, means this should not be dismissed as low-risk in high-privilege environments.

Affected systems

Red Hat Enterprise Linux systems (multiple versions) and Fedora Project systems running SSSD are affected. Any deployment using SSSD's PAM responder for YubiKey or smartcard authentication is vulnerable. The flaw affects the SSSD daemon itself, so all configurations relying on SSSD for smartcard-based authentication—common in enterprise environments with security token requirements—are in scope.

Exploitability

Exploitation requires local access to the target system; remote exploitation is not possible. An attacker must be able to interact with the smartcard or YubiKey authentication flow, either by controlling a device or by modifying smartcard contents. Triggering the crash through denial of service is straightforward once local access is achieved. Escalating this to privilege elevation is significantly more difficult and would require additional techniques beyond simply crashing the responder. The high attack complexity (reflected in the CVSS vector) indicates this is not a trivial one-step exploitation; an attacker needs knowledge of SSSD internals and careful crafting of malicious smartcard data.

Remediation

Patches addressing the use-after-free flaw have been released by Red Hat and Fedora. Organizations should prioritize updating SSSD to patched versions across all systems, especially those handling smartcard or YubiKey authentication. Verify specific patched versions through the respective vendor advisories. As an interim mitigation, consider restricting smartcard/YubiKey authentication to trusted users or limiting local access to systems where such authentication is enabled, though these do not eliminate the underlying vulnerability.

Patch guidance

Check Red Hat's security advisories and Fedora's update repositories for SSSD patches released following this vulnerability's disclosure (June 2026). Update SSSD via your distribution's package manager once patches are available. Test in a non-production environment first, particularly if SSSD is critical to your authentication workflow, to ensure the update does not introduce regression. Verify the patched SSSD version resolves the use-after-free condition before deploying to production systems handling mission-critical authentication.

Detection guidance

Monitor system logs and authentication service logs for unexpected crashes of the SSSD PAM responder (look for segmentation faults or abnormal termination). Alert on repeated authentication failures when users attempt to use smartcard or YubiKey authentication. Watch for suspicious smartcard or YubiKey activity in environments where users have untrusted local access. SIEM rules correlating PAM responder crashes with smartcard authentication attempts can help identify exploitation attempts. Intrusion detection systems may flag attempts to manipulate device data if such behavior is profiled.

Why prioritize this

This vulnerability should be prioritized for patching in environments where YubiKey or smartcard authentication via SSSD is actively used, or where such authentication may be rolled out. The medium CVSS score combined with local-only access requirement means it is not critically urgent for all deployments, but for organizations investing in hardware-based authentication security, the denial-of-service impact and privilege escalation potential warrant timely patching. Patch within 30–60 days unless your environment has high reliance on smartcard authentication, in which case expedite to 2–3 weeks.

Risk score, explained

The CVSS v3.1 score of 6.4 (MEDIUM) balances several factors: high impact across confidentiality, integrity, and availability (all rated high in the vector); however, the attack vector is local-only and attack complexity is high, which constrains the overall score. No privileges are required to trigger the crash (PR:H refers to the attacker's prior privileges, not required escalation), and user interaction is not needed. The score appropriately reflects that while the flaw is serious in its impact potential, it requires attacker sophistication and local presence to exploit, preventing a higher critical or high rating.

Frequently asked questions