CVE-2026-64239
Received Received - Intake

Use-After-Free in Linux Kernel DAMON Sysfs

Publication date: 2026-07-24

Last updated on: 2026-07-24

Assigner: kernel.org

Description
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 > 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.

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Meta Information

Published
2026-07-24
Last Modified
2026-07-24
Generated
2026-07-24
AI Q&A
2026-07-24
EPSS Evaluated
N/A
NVD
CVE-2026-64239
EUVD
EUVD-2026-48648

Affected Vendors & Products

Showing 1 associated CPE
Vendor Product Version / Range
linux linux_kernel *

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Exploitability

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CWE ID Description
CWE-UNKNOWN

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Executive Summary

This vulnerability is a use-after-free issue in the Linux kernel's DAMON sysfs component. It occurs when the kobject release callback is delayed, causing the linked list of region directories to contain freed objects. When new regions are created during this delay, the list can become corrupted, leading to a use-after-free condition.

Detection Guidance

This vulnerability is specific to the Linux kernel's DAMON sysfs component and requires kernel debugging features like CONFIG_DEBUG_KOBJECT_RELEASE to be enabled. Detection involves checking for use-after-free errors in kernel logs after triggering the issue. Run: dmesg | grep underflow after executing the reproduction steps mentioned in the CVE description.

Impact Analysis

This vulnerability can cause system instability, crashes, or potential privilege escalation if exploited. It requires specific kernel configurations (CONFIG_DEBUG_KOBJECT_RELEASE) and specific user actions to trigger, making it unlikely in normal scenarios but possible in debug environments.

Compliance Impact

This vulnerability does not directly affect compliance with standards like GDPR or HIPAA as it is a low-level kernel memory management issue specific to the DAMON sysfs subsystem. It does not involve data exposure, unauthorized access, or privacy violations that these regulations typically address.

Mitigation Strategies

Apply the kernel patch that fixes the issue by removing the region object from the list when decrementing the reference count. Ensure your kernel is updated to a version that includes this fix. Avoid using kernels built with CONFIG_DEBUG_KOBJECT_RELEASE if possible.

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