CVE-2026-31556: 
Linux Kernel vulnerability analysis and mitigation

CVE-2026-31556 is a lock-handling flaw in the Linux kernel's XFS filesystem quota scrub subsystem. The vulnerability exists in the xchk_quota_item function, which can return early after calling xchk_fblock_process_error without releasing the dquot lock (dq->q_qlock), risking lock leaks and deadlocks in subsequent quota operations. It affects Linux kernel versions 6.8.1 through 6.12.79, 6.13 through 6.18.20, 6.19 through 6.19.10, and 7.0 release candidates (rc1–rc7). The vulnerability was disclosed on April 24, 2026, and carries a CVSS v3.1 base score of 5.5 (Medium) (Red Hat CVE, Red Hat Bugzilla).

The root cause is classified as CWE-772 (Missing Release of Resource after Effective Lifetime). In the xchk_quota_item function within the XFS scrub subsystem, when xchk_fblock_process_error returns false, the function exits immediately without calling the corresponding unlock on dq->q_qlock. This unreleased mutex lock can cause subsequent quota operations to block indefinitely, leading to deadlocks. The attack vector is local, requiring low privileges, and no user interaction is needed. The fix involves explicitly unlocking dq->q_qlock before any early return path in the affected function (Red Hat Bugzilla, Red Hat CVE).

Successful exploitation causes the XFS quota subsystem to become unresponsive due to lock leaks or deadlocks, resulting in a denial of service for quota-related filesystem activities and potential degradation of overall system stability. There is no confidentiality or integrity impact; the vulnerability is limited to availability (CVSS availability impact: High). A local attacker with low privileges on a system using XFS with quota enabled could trigger this condition, potentially causing quota operations to hang indefinitely (Red Hat CVE).

There is no known public proof-of-concept exploit and no evidence of in-the-wild exploitation at this time. The vulnerability is not listed in the CISA Known Exploited Vulnerabilities (KEV) catalog. The EPSS score is approximately 0.018% (0.000180), indicating a very low probability of exploitation in the near term. Exploitation requires local access with low privileges, further limiting the practical attack surface (Red Hat CVE).

Update the Linux kernel to one of the patched versions: 6.12.80 or later, 6.18.21 or later, 6.19.11 or later, or 7.0 (stable release). Patch commits are available in the Linux kernel stable repository. Systems with high XFS quota subsystem usage should be prioritized for patching to prevent potential deadlocks and service degradation. No configuration-based workaround is documented; upgrading to a fixed kernel version is the recommended remediation (Red Hat CVE, Red Hat Bugzilla).