CVE-2025-39817

HighCVSS 7.1/10Last modified Oct 19, 2026

Description

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.

Metrics

CVSS 3.1 7.1/10CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H

Weakness enumeration

CWE-125

Affected software

VendorProductVersions
LinuxLinux>= da27a24383b2b10bf6ebd0db29b325548aafecb4, < 0f63fbabeaaaaaaf5b742a2f4c1b4590d50bf1f6; >= da27a24383b2b10bf6ebd0db29b325548aafecb4, < 794399019301944fd6d2e0d7a51b3327e26c410e; >= da27a24383b2b10bf6ebd0db29b325548aafecb4, < 568e7761279b99c6daa3002290fd6d8047ddb6d2; >= da27a24383b2b10bf6ebd0db29b325548aafecb4, < d7f5e35e70507d10cbaff5f9e194ed54c4ee14f7; >= da27a24383b2b10bf6ebd0db29b325548aafecb4, < 925599eba46045930b850a98ae594d2e3028ac40; >= da27a24383b2b10bf6ebd0db29b325548aafecb4, < c2925cd6207079c3f4d040d082515db78d63afbf; >= da27a24383b2b10bf6ebd0db29b325548aafecb4, < 71581a82f38e5a4d807d71fc1bb59aead80ccf95; >= da27a24383b2b10bf6ebd0db29b325548aafecb4, < a6358f8cf64850f3f27857b8ed8c1b08cfc4685c; 688289c4b745c018b3449b4b4c5a2030083c8eaf; >= 3.8.2, < 3.9
LinuxLinux3.9
SiemensSIMATIC CN 4100< V5.0

References

Timeline

Published
Sep 16, 2025
Last modified
Oct 19, 2026
NVD status
Modified

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CVE-2025-39817: High severity, CVSS 7.1 | Vulnix