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🛡️ CVE-2025-39817 — debian-linux

🟠 CVSS 7.1 — High ✅ No Known Exploit CWE-125 NVD
7.1
CVSS Score
0 Low4 Medium7 High9 Critical10

Description

efivarfs: Fix slab-out-of-bounds in efivarfs_d_compare

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

efivarfs: Fix slab-out-of-bounds in efivarfs_d_compare

Observed on kernel 6.6 (present on master as well):

BUG: KASAN: slab-out-of-bounds in memcmp+0x98/0xd0

Call trace:

kasan_check_range+0xe8/0x190

__asan_loadN+0x1c/0x28

memcmp+0x98/0xd0

efivarfs_d_compare+0x68/0xd8

__d_lookup_rcu_op_compare+0x178/0x218

__d_lookup_rcu+0x1f8/0x228

d_alloc_parallel+0x150/0x648

lookup_open.isra.0+0x5f0/0x8d0

open_last_lookups+0x264/0x828

path_openat+0x130/0x3f8

do_filp_open+0x114/0x248

do_sys_openat2+0x340/0x3c0

__arm64_sys_openat+0x120/0x1a0

If dentry->d_name.len < EFI_VARIABLE_GUID_LEN , 'guid' can become

negative, leadings to oob. The issue can be triggered by parallel

lookups using invalid filename:

T1 T2

lookup_open

->lookup

simple_lookup

d_add

// invalid dentry is added to hash list

lookup_open

d_alloc_parallel

__d_lookup_rcu

__d_lookup_rcu_op_compare

hlist_bl_for_each_entry_rcu

// invalid dentry can be retrieved

->d_compare

efivarfs_d_compare

// oob

Fix it by checking 'guid' before cmp.

How this vulnerability can be exploited

This issue can be reached with local access to the system, attack complexity is low, an attacker needs low-level privileges on the target. No user interaction is required. The scope is unchanged, so the impact stays within the vulnerable component. Rated impact: confidentiality high, integrity none, availability high.

Weakness class

CVE-2025-39817 is classified as CWE-125: Out-of-bounds Read. The code reads past the limits of a buffer, exposing adjacent memory contents or crashing the process.

Affected software

CVE-2025-39817 is recorded against 3 packages.

  • debian-linux
  • kernel (from 6.13.0 up to 6.16.5)
  • linux-kernel

Timeline and source

Published on 16 September 2025 and last revised on 30 July 2026. No public exploit is currently recorded for this entry. A vendor advisory or fix has been published. Record sourced from NVD.

References

git.kernel.org
git.kernel.org
git.kernel.org
git.kernel.org
git.kernel.org
git.kernel.org
git.kernel.org
git.kernel.org
lists.debian.org
lists.debian.org
cert-portal.siemens.com

CVE-2025-39817 on other distributions

Each distribution ships its own build and its own fixed version. Pick the one you run:

Details

Severity HIGH
CVSS Score 7.1
CVSS Vector CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H
CWE CWE-125
Public Exploit ✅ No
Source NVD
Published 2025-09-16
Updated 2026-08-20
Modified 2026-07-30

Affected Packages

Software From version Fixed in
debian-linux — —
kernel 6.13.0 6.16.5
linux-kernel — —

References

Similar Threats

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