CVE-2025-39877 [High] | Use-After-Free in Linux Kernel

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.

#	Date	Old EPSS score	New EPSS score	Delta (New - Old)
1	2025-09-23	—	0.02%	—

Date

Old EPSS score

New EPSS score

Delta (New - Old)

2025-09-23

—

0.02%

—

Base score	Version	Severity	Vector	Exploitability	Impact	Score source
7.8	3.1	HIGH	`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H` Click to expand Attack vector (AV:L) They already need access on the box, or another person has to do something wrong; it’s not a remote drive-by. Attack complexity (AC:L) Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup. Privileges required (PR:L) A normal user session is enough; they don’t have to be admin. User interaction (UI:N) Nobody has to click “OK” or open a trap file; it can work without a victim helping. Scope (S:U) Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems. Confidentiality (C:H) Serious risk that confidential data gets exposed in a big way. Integrity (I:H) They could widely tamper with or forge data—trust in the data is badly hurt. Availability (A:H) Could take the service down hard or make it unusable for people who depend on it.	1.8	5.9	[email protected]

Base score

Version

Severity

Vector

Exploitability

Impact

Score source

7.8

3.1

HIGH

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

Attack vector (AV:L): They already need access on the box, or another person has to do something wrong; it’s not a remote drive-by.
Attack complexity (AC:L): Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:L): A normal user session is enough; they don’t have to be admin.
User interaction (UI:N): Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U): Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H): Serious risk that confidential data gets exposed in a big way.
Integrity (I:H): They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H): Could take the service down hard or make it unusable for people who depend on it.

1.8

5.9

[email protected]

OS Trackers for CVE-2025-39877

vendor	priority	summary	link
`debian`	unimportant	CVE-2025-39877 unimportant priority: Debian including 2 source packages (linux, linux-6.1), 6 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 6.	https://security-tracker.debian.org/tracker/CVE-2025-39877
`redhat`	medium	—	https://access.redhat.com/security/cve/CVE-2025-39877
`suse`	medium	CVE-2025-39877 severity moderate: SUSE including 94 source package names (cluster-md-kmp-64kb-6.12.0-160000.6.1, cluster-md-kmp-default, …), 476 product×package rows across 84 product lines (Image SLES-Azure-3P, Image SLES-Azure-Basic, … (84 product lines)): Known Not Affected 278, Fixed 177, First Fixed 21.	https://www.suse.com/security/cve/CVE-2025-39877/
`ubuntu`	medium	CVE-2025-39877 medium priority: Ubuntu including 158 source packages (linux, linux-allwinner-5.19, …), 1414 status rows across 9 suites (bionic, focal, jammy, noble, plucky, questing, trusty, upstream, xenial): DNE 1017, ignored 180, released 117, needed 80, not-affected 16, needs-triage 2, pending 2.	https://ubuntu.com/security/CVE-2025-39877

Affected software / configurations for CVE-2025-39877

Vendor	Product	Version	Raw CPE
linux	linux_kernel	>= 5.18, < 6.1.153	cpe:2.3:o:linux:linux_kernel::::::::
linux	linux_kernel	>= 6.2, < 6.6.107	cpe:2.3:o:linux:linux_kernel::::::::
linux	linux_kernel	>= 6.7, < 6.12.48	cpe:2.3:o:linux:linux_kernel::::::::
linux	linux_kernel	>= 6.13, < 6.16.8	cpe:2.3:o:linux:linux_kernel::::::::
linux	linux_kernel	6.17	cpe:2.3:o:linux:linux_kernel:6.17:rc1::::::
linux	linux_kernel	6.17	cpe:2.3:o:linux:linux_kernel:6.17:rc2::::::
linux	linux_kernel	6.17	cpe:2.3:o:linux:linux_kernel:6.17:rc3::::::
linux	linux_kernel	6.17	cpe:2.3:o:linux:linux_kernel:6.17:rc4::::::
linux	linux_kernel	6.17	cpe:2.3:o:linux:linux_kernel:6.17:rc5::::::
debian	debian_linux	11.0	cpe:2.3:o:debian:debian_linux:11.0:::::::*

References for CVE-2025-39877

URL	Tags
https://git.kernel.org/stable/c/26d29b2ac87a2989071755f9828ebf839b560d4c	Patch
https://git.kernel.org/stable/c/3260a3f0828e06f5f13fac69fb1999a6d60d9cff	Patch
https://git.kernel.org/stable/c/3858c44341ad49dc7544b19cc9f9ecffaa7cc50e	Patch
https://git.kernel.org/stable/c/4e87f461d61959647464a94d11ae15c011be58ce	Patch
https://git.kernel.org/stable/c/60d7a3d2b985a395318faa1d88da6915fad11c19	Patch
https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html	Mailing List Third Party Advisory

URL

CVE-2025-39877 | mm/damon/sysfs: fix use-after-free in state_show()

Exploit prediction scoring system (EPSS) score for CVE-2025-39877

Common vulnerability scoring system (CVSS) metrics for CVE-2025-39877

Weakness enumeration for CVE-2025-39877

OS Trackers for CVE-2025-39877

Affected software / configurations for CVE-2025-39877

References for CVE-2025-39877