High 7.1Published Sep 16, 2025

CVE-2025-39817efivarfs: Fix slab-out-of-bounds in efivarfs_d_compare

Updated under an hour ago (Oct 27, 2026, 12:40 PM ET)

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Exploited in the last 30 days

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.

CVSS: 7.1 HIGH (v3.1, CNA)CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H
Weakness (CWE): Not given
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): Not loaded for this CVE
Assigned by: Linux
NVD analysis: Modified
Record last updated: Aug 5, 2026
First seen by InfoSec Signals: Oct 19, 2026

Affected products

Affected products

Linux Linux linux:linux (from the name)	from da27a24383b2b10bf6ebd0db29b325548aafecb4 before 0f63fbabeaaaaaaf5b742a2f4c1b4590d50bf1f6; from da27a24383b2b10bf6ebd0db29b325548aafecb4 before 794399019301944fd6d2e0d7a51b3327e26c410e; from da27a24383b2b10bf6ebd0db29b325548aafecb4 before 568e7761279b99c6daa3002290fd6d8047ddb6d2; from da27a24383b2b10bf6ebd0db29b325548aafecb4 before d7f5e35e70507d10cbaff5f9e194ed54c4ee14f7; from da27a24383b2b10bf6ebd0db29b325548aafecb4 before 925599eba46045930b850a98ae594d2e3028ac40; from da27a24383b2b10bf6ebd0db29b325548aafecb4 before c2925cd6207079c3f4d040d082515db78d63afbf; from da27a24383b2b10bf6ebd0db29b325548aafecb4 before 71581a82f38e5a4d807d71fc1bb59aead80ccf95; from da27a24383b2b10bf6ebd0db29b325548aafecb4 before a6358f8cf64850f3f27857b8ed8c1b08cfc4685c; and 2 more ranges	CNA record
Siemens SIMATIC CN 4100 siemens:simatic_cn_4100 (from the name)	before V5.0	CISA ADP
linux linux_kernel linux:linux_kernel	from 3.8.2 before 5.4.298; from 5.5 before 5.10.242; from 5.11 before 5.15.191; from 5.16 before 6.1.150; from 6.2 before 6.6.104; from 6.7 before 6.12.45; from 6.13 before 6.16.5; 6.17; and 2 more ranges	NVD
debian debian_linux debian:debian_linux	11.0	NVD

References

References

https://git.kernel.org/stable/c/0f63fbabeaaaaaaf5b742a2f4c1b4590d50bf1f6	patch
https://git.kernel.org/stable/c/794399019301944fd6d2e0d7a51b3327e26c410e	patch
https://git.kernel.org/stable/c/568e7761279b99c6daa3002290fd6d8047ddb6d2	patch
https://git.kernel.org/stable/c/d7f5e35e70507d10cbaff5f9e194ed54c4ee14f7	patch
https://git.kernel.org/stable/c/925599eba46045930b850a98ae594d2e3028ac40	patch
https://git.kernel.org/stable/c/c2925cd6207079c3f4d040d082515db78d63afbf	patch
https://git.kernel.org/stable/c/71581a82f38e5a4d807d71fc1bb59aead80ccf95	patch
https://git.kernel.org/stable/c/a6358f8cf64850f3f27857b8ed8c1b08cfc4685c	patch
https://lists.debian.org/debian-lts-announce/2025/10/msg00007.html	third-party-advisory
https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html	third-party-advisory
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The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.