CyberSecBulletin
CVE-2025-39823NVD status: Modified

Linux: Improper Validation of Array Index

Published Updated By the CyberSecBulletin desk

CVE-2025-39823 is a high-severity improper validation of array index vulnerability in Linux, with a CVSS 3.1 base score of 7.8 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 72777fc31aa7ab2ce00f44bfa3929c6eabbeaf48, 31a0ad2f60cb4816e06218b63e695eb72ce74974, d51e381beed5e2f50f85f49f6c90e023754efa12 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 0.18% 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 72777fc31aa7ab2ce00f44bfa3929c6eabbeaf48 or 31a0ad2f60cb4816e06218b63e695eb72ce74974 or d51e381beed5e2f50f85f49f6c90e023754efa12 or 33e974c2d5a82b2f9d9ba0ad9cbaabc1c8e3985f, 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
LinuxLinux4180bf1b655a791a0a6ef93a2ffffc762722c782 up to, but not including, 72777fc31aa7ab2ce00f44bfa3929c6eabbeaf48; 4180bf1b655a791a0a6ef93a2ffffc762722c782 up to, but not including, 31a0ad2f60cb4816e06218b63e695eb72ce74974; 4180bf1b655a791a0a6ef93a2ffffc762722c782 up to, but not including, d51e381beed5e2f50f85f49f6c90e023754efa12; 4180bf1b655a791a0a6ef93a2ffffc762722c782 up to, but not including, 33e974c2d5a82b2f9d9ba0ad9cbaabc1c8e3985f; 4180bf1b655a791a0a6ef93a2ffffc762722c782 up to, but not including, f49161646e03d107ce81a99c6ca5da682fe5fb69; 4180bf1b655a791a0a6ef93a2ffffc762722c782 up to, but not including, 67a05679621b7f721bdba37a5d18665d3aceb695; 4180bf1b655a791a0a6ef93a2ffffc762722c782 up to, but not including, f57a4bd8d6cb5af05b8ac1be9098e249034639fb; 4180bf1b655a791a0a6ef93a2ffffc762722c782 up to, but not including, c87bd4dd43a624109c3cc42d843138378a7f4548; and 1 more ranges72777fc31aa7ab2ce00f44bfa3929c6eabbeaf48, 31a0ad2f60cb4816e06218b63e695eb72ce74974, d51e381beed5e2f50f85f49f6c90e023754efa12, 33e974c2d5a82b2f9d9ba0ad9cbaabc1c8e3985f, f49161646e03d107ce81a99c6ca5da682fe5fb69, 67a05679621b7f721bdba37a5d18665d3aceb695
SiemensSIMATIC CN 4100before V5.0V5.0
LinuxLinux Kernel4.19 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
HighData or code can be modified at will.
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:H/A:H. Scored by NVD.

Official description

In the Linux kernel, the following vulnerability has been resolved: KVM: x86: use array_index_nospec with indices that come from guest min and dest_id are guest-controlled indices. Using array_index_nospec() after the bounds checks clamps these values to mitigate speculative execution side-channels.

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

The underlying weakness: Improper Validation of Array Index

The product uses untrusted input when calculating or using an array index, but the product does not validate or incorrectly validates the index to ensure the index references a valid position within the array.

How developers prevent this class of flaw

  • Use an input validation framework such as Struts or the OWASP ESAPI Validation API. Note that using a framework does not automatically address all input validation problems; be mindful of weaknesses that could arise from misusing the framework itself (CWE-1173).
  • Use a language that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. For example, Ada allows the programmer to constrain the values of a variable and languages such as Java and Ruby will allow the programmer to handle exceptions when an out-of-bounds index is accessed.
  • Use a CPU and operating system that offers Data Execution Protection (using hardware NX or XD bits) or the equivalent techniques that simulate this feature in software, such as PaX. These techniques ensure that any instruction executed is exclusively at a memory address that is part of the code segment. For more information on these techniques see D3-PSEP (Process Segment Execution Prevention) from D3FEND.

More Improper Validation of Array Index vulnerabilities (CWE-129)

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

Third-party and government advisories

Recent Improper Validation of Array Index vulnerabilities

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