CVE-2026-89989: Linux Kernel Use-After-Free Vulnerability

CVE-2026-89989 Overview

CVE-2026-89989 is a Linux kernel vulnerability in the Integrity Measurement Architecture (IMA) subsystem. The flaw resides in validate_hash_algo(), which passes the return value of dentry_path() directly to integrity_audit_msg() without checking for error pointers. When a file path exceeds the caller's buffer, dentry_path() returns ERR_PTR(-ENAMETOOLONG), which is not NULL. Downstream code then invokes strlen() on the invalid pointer, triggering an unhandled page fault in kernel context.

Critical Impact
A local user setting an extended attribute (setxattr) on a file with a sufficiently long path can crash the kernel, producing a denial-of-service condition on systems with IMA enabled.

Affected Products

Linux kernel branches containing the IMA validate_hash_algo() path check
Distributions shipping affected stable kernel releases
Systems with the Integrity Measurement Architecture (IMA) enabled

Discovery Timeline

2026-09-16 - CVE-2026-89989 published to NVD
2026-09-16 - Last updated in NVD database

Technical Details for CVE-2026-89989

Vulnerability Analysis

The defect is a missing error-pointer check in the IMA subsystem's validate_hash_algo() function. Linux kernel helpers frequently return ERR_PTR() encoded pointers to signal failure. Callers must use IS_ERR() before dereferencing. In this case, dentry_path() returns ERR_PTR(-ENAMETOOLONG) when the resolved path exceeds the provided buffer.

validate_hash_algo() forwards the returned pointer to integrity_audit_msg(), which routes it to audit_log_untrustedstring(). That helper invokes strlen() on the pointer. Because ERR_PTR(-ENAMETOOLONG) decodes to the address 0xffffffffffffffdc, strlen() faults in kernel mode. The reported call trace terminates in ima_inode_setxattr+0x512/0x5f0, confirming the fault is reachable through extended-attribute operations.

The upstream fix adds an IS_ERR() check and substitutes NULL for error pointers, which causes the audit layer to skip the name= field rather than crash.

Root Cause

The root cause is a null pointer dereference class defect stemming from unchecked use of an ERR_PTR() return value. IMA code assumed dentry_path() returned either a valid pointer or NULL, but the kernel API returns encoded error pointers on failure.

Attack Vector

Exploitation requires local access to a system with IMA active. A user with permission to invoke setxattr() on a file located at a very long path can trigger ima_inode_setxattr(), reach validate_hash_algo(), and force the fault. No memory corruption or privilege escalation primitive is described. The observed impact is a kernel oops leading to denial of service. See the applicable Kernel Patch 0de5b525 for the fixed code path.

No verified proof-of-concept code is published. Refer to the upstream commits for the exact code paths and fix.

Detection Methods for CVE-2026-89989

Indicators of Compromise

Kernel oops messages referencing strlen, audit_log_untrustedstring, integrity_audit_message, and ima_inode_setxattr in the call trace.
Page fault entries for the address ffffffffffffffdc in dmesg or /var/log/kern.log.
Unexpected reboots or task crashes on IMA-enabled hosts following setxattr activity.

Detection Strategies

Monitor kernel ring buffer and syslog for BUG: unable to handle page fault entries originating in the IMA code path.
Correlate audit records for setxattr operations on unusually deep or long file paths with subsequent kernel faults.
Track running kernel versions against the fixed stable releases referenced by the upstream patches.

Monitoring Recommendations

Aggregate dmesg and audit subsystem logs centrally to identify repeated IMA-related faults across the fleet.
Alert on any ima_inode_setxattr frame appearing in a kernel crash trace.
Include IMA-enabled hosts in patch compliance dashboards and flag hosts still running vulnerable kernel builds.

How to Mitigate CVE-2026-89989

Immediate Actions Required

Apply the upstream stable kernel updates that add the IS_ERR() check in validate_hash_algo().
Inventory hosts with IMA enabled (CONFIG_IMA=y) and prioritize them for patching.
Restrict local shell access on affected systems until patched kernels are deployed.

Patch Information

The fix is available in multiple stable branches. Apply the commit corresponding to your kernel series:

Workarounds

Disable IMA policies that trigger ima_inode_setxattr evaluation where operationally feasible.
Limit user ability to create files at pathological path depths through filesystem quotas and mount-point layout.
Restrict CAP_SYS_ADMIN and general local access on multi-tenant systems until the kernel is updated.