Use After Free Affecting kernel6.12-tools package, versions <1:6.12.114-139.210.amzn2023


Severity

Recommended
high

Based on Amazon Linux security rating.

Threat Intelligence

EPSS
0.64% (51st percentile)

Do your applications use this vulnerable package?

In a few clicks we can analyze your entire application and see what components are vulnerable in your application, and suggest you quick fixes.

Test your applications
  • Snyk IDSNYK-AMZN2023-KERNEL612TOOLS-22397607
  • published10 Nov 2026
  • disclosed11 Sept 2026

Introduced: 11 Sep 2026

CVE-2026-89654  (opens in a new tab)
CWE-416  (opens in a new tab)

How to fix?

Upgrade Amazon-Linux:2023 kernel6.12-tools to version 1:6.12.114-139.210.amzn2023 or higher.
This issue was patched in ALAS2023-2026-3402.

NVD Description

Note: Versions mentioned in the description apply only to the upstream kernel6.12-tools package and not the kernel6.12-tools package as distributed by Amazon-Linux. See How to fix? for Amazon-Linux:2023 relevant fixed versions and status.

In the Linux kernel, the following vulnerability has been resolved:

ceph: fix UAF in check_new_map() on session freed during unlock

check_new_map() iterates mdsc->sessions[] and for each active session drops mdsc->mutex to perform per-session operations. The forced-close path (rank removed from map) correctly takes a reference on s via ceph_get_mds_session() before releasing mdsc->mutex, but three other paths do not:

Path A (address changed): mutex_unlock → mutex_lock(&s->s_mutex) Path B (reconnect): mutex_unlock → send_mds_reconnect(mdsc, s) Path C (active transition): mutex_unlock → mutex_lock(&s->s_mutex)

Without the extra reference, another thread can acquire mdsc->mutex during the unlock window, call __unregister_session() which drops the last reference on s, and free it. The original thread then accesses freed memory via s->s_mutex.

Fix by adding ceph_get_mds_session(s) before each mutex_unlock and ceph_put_mds_session(s) after the corresponding mutex_lock, matching the pattern already used in the forced-close path.

Race timeline (Path A):

Thread A (check_new_map) Thread B (another map update holds mdsc->mutex or session teardown)


s = mdsc->sessions[i] (refcount == 1, held only by sessions[] array)

mutex_unlock(&mdsc->mutex) ---> acquires mdsc->mutex __unregister_session(mdsc, s) sessions[i] = NULL ceph_put_mds_session(s) refcount: 1 -> 0 kfree(s) <--- freed!

mutex_lock(&s->s_mutex) UAF on freed s->s_mutex

CVSS Base Scores

version 3.1