CVE-2026-109971: Clevis PKCS#11 Information Disclosure

CVE-2026-109971 Overview

CVE-2026-109971 is an information disclosure flaw in the Clevis PKCS#11 pin. The clevis-decrypt-pkcs11 script passes the PKCS#11 token PIN as a command-line argument to pkcs11-tool. Any local user on the system can read this argument through standard process listing utilities or by inspecting the /proc filesystem. The flaw is categorized under [CWE-214] Invocation of Process Using Visible Sensitive Information.

Critical Impact
Local users can harvest PKCS#11 token PINs during Clevis decryption operations, undermining the confidentiality of hardware-backed cryptographic tokens used for disk unlocking and secret management.

Affected Products

Clevis (PKCS#11 pin component)
clevis-decrypt-pkcs11 script
Red Hat distributions shipping the affected Clevis package

Discovery Timeline

2026-10-14 - CVE CVE-2026-109971 published to NVD
2026-10-14 - Last updated in NVD database

Technical Details for CVE-2026-109971

Vulnerability Analysis

Clevis is an automated decryption framework used to unlock encrypted volumes with external key material, including PKCS#11-compatible hardware tokens. The clevis-decrypt-pkcs11 helper invokes pkcs11-tool to interact with the token during decryption.

The helper supplies the user PIN by appending it directly to the pkcs11-tool command line. On Linux systems, process arguments are world-readable through /proc/<pid>/cmdline and surface in output from ps, top, and similar utilities. Any unprivileged local account can poll these interfaces while a decryption operation runs and capture the plaintext PIN.

Exposure of a PKCS#11 PIN allows an attacker who later gains physical or logical access to the token to perform cryptographic operations as the legitimate user. In environments where Clevis automates disk unlocking at boot or during provisioning, PIN disclosure weakens the trust boundary that hardware tokens are expected to provide.

Root Cause

The root cause is insecure handling of sensitive credentials during subprocess invocation. The script passes the PIN as an argv parameter instead of using a non-visible channel such as standard input, an environment variable restricted to the child, or the --pin-source file-reference option supported by pkcs11-tool.

Attack Vector

Exploitation requires local access with low privileges and no user interaction. An attacker runs a loop that reads /proc/*/cmdline or executes ps -ef while Clevis performs a decryption, capturing the PIN at the moment pkcs11-tool is invoked. Attack complexity is elevated because the attacker must observe the narrow window in which the process is active.

No verified exploit code is published. See the Red Hat CVE-2026-109971 Advisory and Red Hat Bug Report #2550363 for vendor technical details.

Detection Methods for CVE-2026-109971

Indicators of Compromise

Unexpected processes from non-administrative users reading /proc/*/cmdline or spawning repeated ps, pgrep, or cat /proc/*/cmdline invocations.
Shell scripts or binaries polling the process table at high frequency on hosts that run Clevis decryption.
Audit records showing pkcs11-tool executions whose argv includes a --pin or -p parameter followed by a literal value.

Detection Strategies

Enable Linux Audit (auditd) rules on execve to capture full command lines of pkcs11-tool and clevis-decrypt-pkcs11.
Alert when non-root users read /proc/<pid>/cmdline for processes owned by other users, especially during known decryption windows.
Correlate process-table scanning behavior with subsequent token or key usage from the same account.

Monitoring Recommendations

Centralize auditd and shell history logs for systems running Clevis and review them for argv-based secret exposure patterns.
Monitor privileged service accounts that invoke Clevis for anomalous child processes or credential access attempts.

How to Mitigate CVE-2026-109971

Immediate Actions Required

Apply the vendor-provided Clevis update once released by your distribution. Track status through the Red Hat CVE-2026-109971 Advisory.
Restrict local shell access on hosts where Clevis performs PKCS#11 decryption to reduce the pool of users able to read process arguments.
Rotate any PKCS#11 token PINs that may have been exposed on multi-user systems.

Patch Information

At publication, the Red Hat advisory tracks remediation status for affected packages. Consult your distribution's errata for the fixed Clevis version and apply updates through the standard package manager.

Workarounds

Mount /proc with the hidepid=2 option so unprivileged users cannot inspect other users' process arguments.
Limit interactive logins on hosts performing Clevis-based decryption and enforce least privilege for service accounts.
Where feasible, substitute PKCS#11 workflows that read the PIN from a protected file via pkcs11-tool --pin-source instead of argv.

bash

# Harden /proc so process cmdlines are not world-readable
# Add to /etc/fstab:
proc    /proc    proc    defaults,hidepid=2,gid=proc    0 0

# Apply without reboot:
mount -o remount,hidepid=2,gid=proc /proc