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Linux KernelOperating system · Linux

CVE-2025-39817

HIGH · 7.1 CVSS v3.1 Published 2025-09-16
Fix available
A fix is available. Upgrade to 5.4.298 / 5.10.242 or later.
See remediation →
73/100
Remediation priority · Elevated
Zero-click Patch available

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis
How this class of weakness works · CWE-125

The code reads past the end (or before the start) of a buffer, returning memory that was never meant to be exposed. Attackers use it to leak secrets like keys or to defeat memory-protection defences. Remediation is validating indices and lengths before every read.

General guidance for the out-of-bounds read class — the official description and references above are authoritative for this specific CVE. Want a bespoke review and a reviewed fix? Ask our team →

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Linux KernelOperating system
Affected:>= 3.8.2, < 5.4.298>= 5.5, < 5.10.242>= 5.11, < 5.15.191>= 5.16, < 6.1.150>= 6.2, < 6.6.104>= 6.7, < 6.12.45>= 6.13, < 6.16.5= 6.17
Debian LinuxOperating system
Affected:= 11.0

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Local
Complexity
Low
Privileges
Low
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
None
Availability
High

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

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 5.4.298 / 5.10.242 / 5.15.191 or later
Fixed in 5.4.2985.10.2425.15.191
Vendor patch git.kernel.org →
Recommended fix High confidence

Upgrade to kernel 5.4.298, 5.10.242, 5.15.191, or 6.1.150 (or later stable releases) depending on your current branch. For Debian 11, apply Debian kernel security updates when available.

  1. Identify your current kernel version using 'uname -r'
  2. Determine which version branch you are on (e.g., 5.4.x, 5.10.x, 5.15.x, 6.1.x)
  3. Upgrade to a fixed kernel version: for 5.4.x branch upgrade to >= 5.4.298, for 5.10.x upgrade to >= 5.10.242, for 5.15.x upgrade to >= 5.15.191, for 6.1.x upgrade to >= 6.1.150
  4. Update your package manager and install the new kernel (e.g., 'apt update && apt upgrade' for Debian, or 'yum update' for RHEL-based systems)
  5. Reboot the system to load the new kernel
  6. Verify the fix is applied by checking the kernel version and confirming efivarfs module loads without errors
Caveat Kernel upgrades require system reboot and may affect proprietary kernel modules or drivers compiled against the old kernel API.

Generated from the published advisory — verify against the referenced sources before acting.

We can perform the upgrade in your staging environment and verify nothing breaks — typical engagement from $3,200. Get the upgrade done

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2025-39817 in production — separate from our analysis above.

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What this is

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What belongs here
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  • Version or environment caveats, and links to real fixes
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