CVE-2025-24032 is a critical vulnerability in the pam_pkcs11 module of OpenSC, a Linux-PAM login module that enables user authentication via X.509 certificates. The vulnerability arises from improper authentication logic when the configuration parameter cert_policy is set to 'none', which is the default setting in versions prior to 0.6.13. Under this configuration, pam_pkcs11 only verifies if the user can log into the token, without validating the private key's signature. This flaw allows an attacker to create a malicious token containing the victim user's public certificate data and a PIN known to the attacker. Since no cryptographic proof of possession of the private key is required, the attacker can authenticate as the victim user by presenting this forged token. The issue affects all pam_pkcs11 versions starting from 0.6.0 up to but not including 0.6.13. The vulnerability was addressed by changing the default cert_policy to require signature verification, ensuring that possession of the private key is validated during login. The CVSS 4.0 score is 9.2 (critical), reflecting the vulnerability's network attack vector, low complexity, no user interaction, and high impact on confidentiality and integrity. No known exploits have been reported in the wild yet, but the ease of exploitation and the critical nature of authentication bypass make this a significant threat to Linux systems relying on pam_pkcs11 for certificate-based authentication.

For European organizations, this vulnerability poses a severe risk to systems that utilize pam_pkcs11 for secure user authentication, particularly in environments where smart cards or hardware tokens with X.509 certificates are employed. Successful exploitation allows attackers to bypass authentication controls and gain unauthorized access to user accounts without needing the private key, potentially leading to privilege escalation, data breaches, and lateral movement within networks. This undermines the trust model of certificate-based authentication, which is often used in high-security sectors such as government, finance, healthcare, and critical infrastructure. The impact is heightened in regulated industries subject to strict compliance requirements (e.g., GDPR, NIS Directive), where unauthorized access could result in significant legal and financial penalties. Additionally, since the vulnerability affects the Linux-PAM stack, it could compromise a wide range of Linux-based servers and workstations commonly deployed across European enterprises and public sector organizations.

Organizations should immediately verify their pam_pkcs11 version and configuration. If running versions prior to 0.6.13, upgrade to version 0.6.13 or later where the default cert_policy enforces signature verification. If upgrading is not immediately feasible, modify the pam_pkcs11 configuration file (pam_pkcs11.conf) to set 'cert_policy = signature;' to require validation of the private key signature during authentication. This change prevents attackers from authenticating with tokens lacking the private key. Additionally, review and audit all systems using pam_pkcs11 to ensure no unauthorized tokens have been introduced. Implement strict token issuance and management policies, including PIN complexity and token lifecycle controls. Monitoring authentication logs for anomalous login attempts involving certificate-based authentication can help detect exploitation attempts. Finally, consider multi-factor authentication mechanisms that do not solely rely on certificate-based login to add defense in depth.