CVE-2025-39877: debian linux Use-After-Free — Fix

Description

In the Linux kernel, the following vulnerability has been resolved: mm/damon/sysfs: fix use-after-free in state_show() state_show() reads kdamond->damon_ctx without holding damon_sysfs_lock. This allows a use-after-free race: CPU 0 CPU 1 ----- ----- state_show() damon_sysfs_turn_damon_on() ctx = kdamond->damon_ctx; mutex_lock(&damon_sysfs_lock); damon_destroy_ctx(kdamond->damon_ctx); kdamond->damon_ctx = NULL; mutex_unlock(&damon_sysfs_lock); damon_is_running(ctx); /* ctx is freed */ mutex_lock(&ctx->kdamond_lock); /* UAF */ (The race can also occur with damon_sysfs_kdamonds_rm_dirs() and damon_sysfs_kdamond_release(), which free or replace the context under damon_sysfs_lock.) Fix by taking damon_sysfs_lock before dereferencing the context, mirroring the locking used in pid_show(). The bug has existed since state_show() first accessed kdamond->damon_ctx.

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CVSS v3.1 Score

7.8

HIGH

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Weakness Type (CWE)

CWE-416 Use After Free

Affected Products

Vendor	Product	Versions
linux	linux_kernel	5.18 — 6.1.153
linux	linux_kernel	6.2 — 6.6.107
linux	linux_kernel	6.7 — 6.12.48
linux	linux_kernel	6.13 — 6.16.8
linux	linux_kernel	All
linux	linux_kernel	All
linux	linux_kernel	All
linux	linux_kernel	All
linux	linux_kernel	All
debian	debian_linux	All

References

Advisories & Patches

https://git.kernel.org/stable/c/26d29b2ac87a2989071755f9828ebf839b560d4c https://git.kernel.org/stable/c/3260a3f0828e06f5f13fac69fb1999a6d60d9cff https://git.kernel.org/stable/c/3858c44341ad49dc7544b19cc9f9ecffaa7cc50e https://git.kernel.org/stable/c/4e87f461d61959647464a94d11ae15c011be58ce https://git.kernel.org/stable/c/60d7a3d2b985a395318faa1d88da6915fad11c19

Other References

https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html

Frequently Asked Questions

What is CVE-2025-39877? +

In the Linux kernel, the following vulnerability has been resolved: mm/damon/sysfs: fix use-after-free in state_show() state_show() reads kdamond->damon_ctx without holding damon_sysfs_lock. This allows a use-after-free race: CPU 0 CPU 1 ----- ----- state_show() damon_sysfs_turn_damon_on() ctx = kdamond->damon_ctx; mutex_lock(&damon_sysfs_lock); damon_destroy_ctx(kdamond->damon_ctx); kdamond->damon_ctx = NULL; mutex_unlock(&damon_sysfs_lock); damon_is_running(ctx); /* ctx is freed */ mutex_lock(&ctx->kdamond_lock); /* UAF */ (The race can also occur with damon_sysfs_kdamonds_rm_dirs() and damon_sysfs_kdamond_release(), which free or replace the context under damon_sysfs_lock.) Fix by taking damon_sysfs_lock before dereferencing the context, mirroring the locking used in pid_show(). The bug has existed since state_show() first accessed kdamond->damon_ctx. It has a CVSS v3.1 base score of 7.8 (HIGH).

How severe is CVE-2025-39877? +

CVE-2025-39877 has a CVSS v3.1 score of 7.8 out of 10, rated HIGH. This is a high-severity vulnerability that should be prioritized for patching.

What products are affected by CVE-2025-39877? +

CVE-2025-39877 affects products from debian, linux, specifically: debian_linux, linux_kernel. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2025-39877? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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