Use After Free Affecting kernel6.18-tools-debuginfo package, versions <1:6.18.35-68.127.amzn2023


Severity

Recommended
high

Based on Amazon Linux security rating.

Threat Intelligence

EPSS
0.12% (2nd 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-KERNEL618TOOLSDEBUGINFO-18905043
  • published18 Aug 2026
  • disclosed24 Jul 2026

Introduced: 24 Jul 2026

NewCVE-2026-64239  (opens in a new tab)
CWE-416  (opens in a new tab)

How to fix?

Upgrade Amazon-Linux:2023 kernel6.18-tools-debuginfo to version 1:6.18.35-68.127.amzn2023 or higher.
This issue was patched in ALAS2023-2026-1881.

NVD Description

Note: Versions mentioned in the description apply only to the upstream kernel6.18-tools-debuginfo package and not the kernel6.18-tools-debuginfo 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:

mm/damon/sysfs-schemes: delete tried region in regions_rmdirs()

DAMON sysfs maintains the DAMOS tried region directory objects via a linked list. When the user requests refresh of the directories, DAMON sysfs removes all the region directories first, and then generate updated regions directory on the empty space. The removal function (damon_sysfs_scheme_regions_rm_dirs()) only puts the kobj objects. Deletion of the container region object from the linked list is done inside the kobj release callback function.

If somehow the callback invocation is delayed, the list will contain regions list that gonna be freed. If the updated region directories creation is started in this situation, the list can be corrupted and use-after-free can happen.

Because the kobj objects are managed by only DAMON sysfs, the issue cannot happen in normal situation. But, such delays can be made on kernels that built with CONFIG_DEBUG_KOBJECT_RELEASE. On the kernel, the issue can indeed be reproduced like below.

# damo start --damos_action stat
# cd /sys/kernel/mm/damon/admin/kdamonds/0/
# for i in {1..10}; do echo update_schemes_tried_regions &gt; state; done
# dmesg | grep underflow
[   89.296152] refcount_t: underflow; use-after-free.

Fix the issue by removing the region object from the list when decrementing the reference count.

Also update damos_sysfs_populate_region_dir() to add the region object to the list only after the kobject_init_and_add() is success, so that fail of kobject_init_and_add() is not leaving the deallocated object on the list.

The issue was discovered [1] by Sashiko.

CVSS Base Scores

version 3.1