CVE-2025-24531 is a vulnerability identified in the OpenSC project's pam_pkcs11 module, specifically affecting versions prior to 0.6.13. The issue arises from the pam_sm_authenticate() function, which is responsible for handling authentication requests using smartcards. In error scenarios—such as when a smartcard triggers an error before login—the function incorrectly returns the status code PAM_IGNORE instead of an appropriate failure code. According to the PAM (Pluggable Authentication Module) framework, returning PAM_IGNORE signals that the module should be skipped, effectively allowing the authentication process to continue without properly validating the smartcard authentication. This behavior creates an authentication bypass vulnerability, permitting an attacker with local access to circumvent authentication controls without needing user interaction or prior privileges. The vulnerability is classified under CWE-393 (Return of Wrong Status Code), indicating improper error handling that leads to security issues. The CVSS v3.1 base score is 6.7 (medium severity), with an attack vector of local (AV:L), high attack complexity (AC:H), no privileges required (PR:N), no user interaction (UI:N), unchanged scope (S:U), and high impact on confidentiality and integrity (C:H/I:H/A:N). This means exploitation requires local access and is complex but can lead to significant unauthorized access and data compromise. No public exploits or active exploitation in the wild have been reported to date. The vulnerability affects systems relying on pam_pkcs11 for smartcard authentication, commonly used in secure environments requiring multi-factor authentication. The fix involves correcting the return codes in pam_sm_authenticate() to ensure errors do not result in PAM_IGNORE, thereby enforcing proper authentication failure handling. Although no patch links are currently provided, upgrading to version 0.6.13 or later when available is recommended.

For European organizations, especially those in government, defense, finance, and critical infrastructure sectors that utilize smartcard-based authentication via pam_pkcs11, this vulnerability poses a significant risk. An attacker with local access could bypass authentication controls, potentially gaining unauthorized access to sensitive systems and data. This compromises confidentiality and integrity, enabling data theft, unauthorized transactions, or system manipulation. The lack of availability impact means systems remain operational but insecure. The requirement for local access limits remote exploitation but insider threats or attackers who gain physical or local system access can exploit this flaw. Given the widespread use of smartcards in European public sector and regulated industries, the vulnerability could undermine trust in authentication mechanisms and compliance with regulations such as GDPR and NIS Directive. The medium severity rating reflects the balance between exploitation difficulty and potential damage.

1. Upgrade pam_pkcs11 to version 0.6.13 or later once the patch is released, as it will correct the improper return code handling in pam_sm_authenticate(). 2. Until a patch is available, implement compensating controls such as restricting local access to systems using pam_pkcs11, enforcing strict physical security, and monitoring authentication logs for anomalies indicating bypass attempts. 3. Conduct thorough audits of smartcard authentication logs to detect unusual authentication successes or failures that may indicate exploitation attempts. 4. Employ multi-factor authentication methods that do not solely rely on pam_pkcs11 or smartcards to reduce risk exposure. 5. Educate system administrators and security teams about this vulnerability to ensure rapid response and incident handling if suspicious activity is detected. 6. Review and harden PAM configuration files to ensure no fallback or alternative authentication methods inadvertently allow bypass. 7. Coordinate with vendors and security communities to obtain patches promptly and validate their effectiveness in test environments before deployment.