CyberSecBulletin
CVE-2026-31666NVD status: Modified

Linux: Improper Check for Unusual or Exceptional Conditions

Published Updated By the CyberSecBulletin desk

CVE-2026-31666 is a high-severity improper check for unusual or exceptional conditions 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 4125a194db4a6cf91f619f38788272651cb97dce, 450e6a685d0cad95b15f8af152057bd0bf79f50b, ab1e022379c3c811aa72da8eb0c7507859a1d0f5 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 0.12% 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 4125a194db4a6cf91f619f38788272651cb97dce or 450e6a685d0cad95b15f8af152057bd0bf79f50b or ab1e022379c3c811aa72da8eb0c7507859a1d0f5 or 316fb1b3169efb081d2db910cbbfef445afa03b9, whichever matches your release line, or a later version.
  2. Update Linux Kernel to 6.12.82 or 6.18.23 or 6.19.13, whichever matches your release line, or a later version.

Affected products and versions

VendorProductAffected versionsFixed in
LinuxLinux1618aa3c2e0163f5ac34d514ae89474521910536 up to, but not including, 4125a194db4a6cf91f619f38788272651cb97dce; 1618aa3c2e0163f5ac34d514ae89474521910536 up to, but not including, 450e6a685d0cad95b15f8af152057bd0bf79f50b; 1618aa3c2e0163f5ac34d514ae89474521910536 up to, but not including, ab1e022379c3c811aa72da8eb0c7507859a1d0f5; 1618aa3c2e0163f5ac34d514ae89474521910536 up to, but not including, 316fb1b3169efb081d2db910cbbfef445afa03b9; 6.104125a194db4a6cf91f619f38788272651cb97dce, 450e6a685d0cad95b15f8af152057bd0bf79f50b, ab1e022379c3c811aa72da8eb0c7507859a1d0f5, 316fb1b3169efb081d2db910cbbfef445afa03b9
LinuxLinux Kernel6.10.1 up to, but not including, 6.12.82; 6.13 up to, but not including, 6.18.23; 6.19 up to, but not including, 6.19.13; 6.10; 7.06.12.82, 6.18.23, 6.19.13

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 CNA.

Official description

In the Linux kernel, the following vulnerability has been resolved: btrfs: fix incorrect return value after changing leaf in lookup_extent_data_ref() After commit 1618aa3c2e01 ("btrfs: simplify return variables in lookup_extent_data_ref()"), the err and ret variables were merged into a single ret variable. However, when btrfs_next_leaf() returns 0 (success), ret is overwritten from -ENOENT to 0. If the first key in the next leaf does not match (different objectid or type), the function returns 0 instead of -ENOENT, making the caller believe the lookup succeeded when it did not. This can lead to operations on the wrong extent tree item, potentially causing extent tree corruption. Fix this by returning -ENOENT directly when the key does not match, instead of relying on the ret variable.

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

The underlying weakness: Improper Check for Unusual or Exceptional Conditions

The product does not check or incorrectly checks for unusual or exceptional conditions that are not expected to occur frequently during day to day operation of the product.

How developers prevent this class of flaw

  • Use a language that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. Choose languages with features such as exception handling that force the programmer to anticipate unusual conditions that may generate exceptions. Custom exceptions may need to be developed to handle unusual business-logic conditions. Be careful not to pass sensitive exceptions back to the user (CWE-209, CWE-248).
  • Check the results of all functions that return a value and verify that the value is expected.
  • If using exception handling, catch and throw specific exceptions instead of overly-general exceptions (CWE-396, CWE-397). Catch and handle exceptions as locally as possible so that exceptions do not propagate too far up the call stack (CWE-705). Avoid unchecked or uncaught exceptions where feasible (CWE-248).

More Improper Check for Unusual or Exceptional Conditions vulnerabilities (CWE-754)

Timeline

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

References

Recent Improper Check for Unusual or Exceptional Conditions vulnerabilities

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