CVE-2026-53287: Linux Kernel Audit Logging Corruption – CAPSET Capability Miscord

Technical summary

The Linux kernel function __audit_log_capset() contains a copy-paste error that writes the effective capability set (cap_effective) into the cap_inheritable field of CAPSET audit records. When the kernel logs capability set changes via the audit subsystem, the process inheritable capability set (cap_pi) is populated with the wrong data. This silently corrupts audit data relied upon for compliance, threat detection, and post-incident forensics. The vulnerability exists in the audit logging layer and does not directly enable privilege escalation, but it enables attackers to mask capability modifications that would otherwise be logged.

Business impact

Organizations relying on Linux audit logs for compliance frameworks (SOC 2, PCI-DSS, ISO 27001) and incident response will have incomplete or misleading capability-related evidence. An attacker exploiting this flaw could modify a process's inheritable capabilities—potentially setting up privilege escalation vectors—without the action appearing correctly in audit records. This undermines forensic reconstruction, violates compliance evidence integrity, and creates blind spots in security monitoring. The 18-year-old nature of this bug means it affects all current and recent Linux distributions and deployments.

Affected systems

All Linux kernel versions from the 2008 introduction of CAPSET audit records through current versions are affected. This includes Red Hat Enterprise Linux, Ubuntu, Debian, SUSE, and all other distributions using the affected kernel code. Any system using the audit subsystem to monitor capability changes is vulnerable to silent audit data corruption.

Exploitability

An attacker with local access and sufficient permissions to modify process capabilities (typically requiring CAP_SYS_ADMIN or equivalent) could deliberately change inheritable capabilities without those changes being properly recorded in the audit log. The vulnerability is not network-exploitable and does not directly grant elevated privileges, but it enables obfuscation of capability modifications that serve as prerequisites for privilege escalation exploits. The bug requires local execution and knowledge of capability manipulation, making it a tool for advanced persistent threat actors or privileged insiders attempting to cover their tracks.

Remediation

Patch the kernel to a version that corrects __audit_log_capset() to record cap_inheritable instead of cap_effective in the inheritable field. Verify against the vendor advisory for specific patched kernel versions for your distribution. After patching, no configuration changes are required. Organizations should also review historical audit logs for any CAPSET records to determine whether capability changes were masked during the vulnerability window.

Patch guidance

Obtain a patched Linux kernel from your distribution vendor that includes the fix for CVE-2026-53287. Verify the specific version numbers against your vendor's security advisory (this will vary by distribution). Apply the kernel update using your distribution's standard package manager and reboot to activate the patched kernel. Test audit logging on a non-production system to confirm CAPSET records now correctly report inheritable capabilities.

Detection guidance

Post-patch, audit logs will correctly reflect inheritable capability changes. Review historical CAPSET audit records (ausearch, auditctl) for any period prior to patching—particularly focusing on accounts that subsequently executed privilege escalation attempts or exploits. Cross-reference capability changes with process execution logs and privilege escalation events to identify any masked modifications. Enable continuous auditing of capability changes (auditctl rules for execve and capset) to catch future anomalies.

Why prioritize this

Although the CVSS score is moderate (5.5), the 18-year window of silent audit data corruption creates significant compliance and forensic risk. This is not an availability or confidentiality flaw, but an integrity issue that specifically undermines logging—the detective control relied upon to identify breach activity. Organizations with strict compliance requirements, mature security monitoring, or forensic needs should prioritize patching to restore audit integrity.

Risk score, explained

The CVSS 3.1 score of 5.5 (MEDIUM, AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H) reflects local-only attack vector, low complexity, requirement for low privileges, and high impact to availability. However, the 'availability' impact here is availability of trustworthy audit data rather than system availability. The lack of confidentiality or integrity impact on the running system itself keeps the score moderate, but the business impact to forensic and compliance capabilities is disproportionately high.

Frequently asked questions