CyberSecBulletin
CVE-2025-39817NVD status: Modified

Linux: Out-of-bounds Read

Published Updated By the CyberSecBulletin desk

CVE-2025-39817 is a high-severity out-of-bounds read vulnerability in Linux, with a CVSS 3.1 base score of 7.1 out of 10. It can be exploited with local access to the system by an attacker with a low-privileged account, without any action from a user. The record lists versions 0f63fbabeaaaaaaf5b742a2f4c1b4590d50bf1f6, 794399019301944fd6d2e0d7a51b3327e26c410e, 568e7761279b99c6daa3002290fd6d8047ddb6d2 as the first without the flaw, so updating Linux to one of those releases or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.17% chance of exploitation within 30 days, which is low compared with other CVEs.

Next patch cycle

High severity with no evidence of exploitation so far.

What to do

  1. Update Linux to 0f63fbabeaaaaaaf5b742a2f4c1b4590d50bf1f6 or 794399019301944fd6d2e0d7a51b3327e26c410e or 568e7761279b99c6daa3002290fd6d8047ddb6d2 or d7f5e35e70507d10cbaff5f9e194ed54c4ee14f7, whichever matches your release line, or a later version.
  2. Update SIMATIC CN 4100 to V5.0 or a later version.
  3. Update Linux Kernel to 5.4.298 or 5.10.242 or 5.15.191 or 6.1.150, whichever matches your release line, or a later version.

Affected products and versions

VendorProductAffected versionsFixed in
LinuxLinuxda27a24383b2b10bf6ebd0db29b325548aafecb4 up to, but not including, 0f63fbabeaaaaaaf5b742a2f4c1b4590d50bf1f6; da27a24383b2b10bf6ebd0db29b325548aafecb4 up to, but not including, 794399019301944fd6d2e0d7a51b3327e26c410e; da27a24383b2b10bf6ebd0db29b325548aafecb4 up to, but not including, 568e7761279b99c6daa3002290fd6d8047ddb6d2; da27a24383b2b10bf6ebd0db29b325548aafecb4 up to, but not including, d7f5e35e70507d10cbaff5f9e194ed54c4ee14f7; da27a24383b2b10bf6ebd0db29b325548aafecb4 up to, but not including, 925599eba46045930b850a98ae594d2e3028ac40; da27a24383b2b10bf6ebd0db29b325548aafecb4 up to, but not including, c2925cd6207079c3f4d040d082515db78d63afbf; da27a24383b2b10bf6ebd0db29b325548aafecb4 up to, but not including, 71581a82f38e5a4d807d71fc1bb59aead80ccf95; da27a24383b2b10bf6ebd0db29b325548aafecb4 up to, but not including, a6358f8cf64850f3f27857b8ed8c1b08cfc4685c; and 3 more ranges0f63fbabeaaaaaaf5b742a2f4c1b4590d50bf1f6, 794399019301944fd6d2e0d7a51b3327e26c410e, 568e7761279b99c6daa3002290fd6d8047ddb6d2, d7f5e35e70507d10cbaff5f9e194ed54c4ee14f7, 925599eba46045930b850a98ae594d2e3028ac40, c2925cd6207079c3f4d040d082515db78d63afbf
SiemensSIMATIC CN 4100before V5.0V5.0
LinuxLinux Kernel3.8.2 up to, but not including, 5.4.298; 5.5 up to, but not including, 5.10.242; 5.11 up to, but not including, 5.15.191; 5.16 up to, but not including, 6.1.150; 6.2 up to, but not including, 6.6.104; 6.7 up to, but not including, 6.12.45; 6.13 up to, but not including, 6.16.5; 6.175.4.298, 5.10.242, 5.15.191, 6.1.150, 6.6.104, 6.12.45
DebianDebian Linux11.0Not stated

Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.

How the severity score breaks down

Attack vector
LocalThe attacker needs local access or must trick a user into running something.
Attack complexity
LowNo special conditions are needed; the attack works reliably.
Privileges required
LowA basic user account is enough.
User interaction
NoneNo action by a victim is required.
Scope
UnchangedImpact stays within the vulnerable component.
Confidentiality
HighAll data handled by the component can be read.
Integrity
NoneNothing can be modified.
Availability
HighThe component can be taken down completely.

Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H. Scored by NVD.

Scoring systemScoreSeverityScored by
CVSS 3.17.1HighCNA
CVSS 3.17.1HighNVD

Official 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.

Source: the CVE record as published by its numbering authority, via NVD and CVE.org.

The underlying weakness: Out-of-bounds Read

The product reads data past the end, or before the beginning, of the intended buffer.

How developers prevent this class of flaw

  • Use a language that provides appropriate memory abstractions.

More Out-of-bounds Read vulnerabilities (CWE-125)

Timeline

  1. CVE record published.
  2. CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: partial).
  3. Record last changed materially (score, affected products, status or references).

References

Recent Out-of-bounds Read vulnerabilities

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