CVE-2026-109968 in Clevis
Summary
by MITRE • 10/14/2026
A flaw was found in the clevis PKCS#11 pin. The clevis-pkcs11-afunix-socket-unlock daemon logs LUKS disk encryption passphrases in plaintext to a log file. The log file is created without restrictive permissions, making it world-readable under the default process umask. A local attacker can read the log file to obtain the LUKS passphrase.
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Analysis
by VulDB Data Team • 10/14/2026
The vulnerability identified within the clevis PKCS#11 pin implementation represents a critical failure in secure credential handling and operating system permission management. Clevis is an automated decryption tool for disk encryption, often used in conjunction with TPMs or network-based key servers to unlock LUKS encrypted volumes without manual intervention. The specific flaw resides in the afunix-socket-unlock daemon component of clevis-pkcs11. This service acts as a bridge between system services requesting volume unlocking and the PKCS#11 token, which stores sensitive cryptographic material such as passphrases or keys. When this daemon processes an unlock request, it inadvertently logs the LUKS disk encryption passphrase in plaintext to a log file for debugging or auditing purposes. While logging can be useful for troubleshooting, recording high-value secrets like full-disk encryption passwords is fundamentally contrary to security best practices and introduces severe risk if those logs are not protected with appropriate access controls.
The technical root cause of this vulnerability lies in the combination of insecure logging behavior and improper file system permissions. The daemon writes the plaintext passphrase directly into a log file without stripping sensitive data or encrypting it before storage. More critically, the log file is created using the default process umask, which typically allows world-readable access on many Linux distributions. This means that any user account on the local system, regardless of privilege level, can read the contents of this log file. In a multi-user environment, such as a shared server or a workstation with multiple users, this creates an immediate and trivial attack vector for credential theft. The attacker does not need to exploit a complex software flaw or gain elevated privileges; they simply need local shell access to execute a standard read command against the exposed log file.
From an operational impact perspective, this vulnerability effectively nullifies the security provided by LUKS disk encryption if the passphrase is compromised via this side channel. An attacker who obtains the plaintext passphrase can decrypt the protected volume at will, gaining full administrative control over the data stored on that drive. This includes access to sensitive personal information, corporate intellectual property, system configurations, and potentially other credentials or keys stored within the decrypted environment. The impact is particularly severe in scenarios where clevis is used for automated boot processes or unattended decryption, as these environments often run with elevated privileges but may have less stringent monitoring of local user activity. Furthermore, because the log file persists on disk, an attacker can review historical logs to harvest passphrases from previous unlock events, extending the window of exposure beyond a single session.
This vulnerability aligns closely with CWE-532, which describes information exposure through log files, and CWE-732, which pertains to incorrect permission assignment for critical resources. The failure to restrict access to sensitive data stored in logs is a common misconfiguration that undermines the principle of least privilege. Additionally, from an offensive security perspective, this scenario maps to ATT&CK technique T1005, Data from Local System, where adversaries collect data directly from local sources without remote execution capabilities. It also touches upon CWE-284, Improper Access Control, as the system fails to enforce appropriate restrictions on who can access sensitive information.
To mitigate this vulnerability, immediate remediation steps should focus on restricting file permissions and altering logging behavior. The log file containing plaintext passphrases must be secured by changing its ownership and permission bits so that only the specific user or group running the clevis daemon has read access. This typically involves using chmod to set restrictive permissions, such as 600, ensuring that other users on the system cannot view the contents. Furthermore, developers should modify the application logic to avoid logging sensitive credentials altogether. If logging is necessary for operational reasons, passphrases and secrets must be redacted or hashed before being written to any log file. System administrators should also audit existing clevis configurations across their infrastructure to identify other instances where this default behavior might expose similar risks. Regular security audits of log files for accidental inclusion of sensitive data are recommended as a broader defensive measure against information leakage vulnerabilities.