CyberSecBulletin
CVE-2026-31637NVD status: Modified

Linux: Improper Check for Unusual or Exceptional Conditions

Published Updated By the CyberSecBulletin desk

CVE-2026-31637 is a critical-severity improper check for unusual or exceptional conditions vulnerability in Linux, with a CVSS 3.1 base score of 9.8 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. The record lists versions 252157d939d179b5d767cb860ff8fa7f8723b67a, a75b3b361dd481d942c5f259a82d59718a41092c, b3a808cd0790b5075aaa2bc3588edf02cd71d352 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 0.59% chance of exploitation within 30 days, which is low compared with other CVEs.

Patch this week

Critical severity: a successful attack would have severe impact.

What to do

  1. Update Linux to 252157d939d179b5d767cb860ff8fa7f8723b67a or a75b3b361dd481d942c5f259a82d59718a41092c or b3a808cd0790b5075aaa2bc3588edf02cd71d352 or 47073aab8a3a5a7b41c9bd37d2a3dcbeeccd6c8a, whichever matches your release line, or a later version.
  2. Update Linux Kernel to 6.6.135 or 6.12.82 or 6.18.23 or 6.19.13, whichever matches your release line, or a later version.
  3. Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.

Affected products and versions

VendorProductAffected versionsFixed in
LinuxLinux17926a79320afa9b95df6b977b40cca6d8713cea up to, but not including, 252157d939d179b5d767cb860ff8fa7f8723b67a; 17926a79320afa9b95df6b977b40cca6d8713cea up to, but not including, a75b3b361dd481d942c5f259a82d59718a41092c; 17926a79320afa9b95df6b977b40cca6d8713cea up to, but not including, b3a808cd0790b5075aaa2bc3588edf02cd71d352; 17926a79320afa9b95df6b977b40cca6d8713cea up to, but not including, 47073aab8a3a5a7b41c9bd37d2a3dcbeeccd6c8a; 17926a79320afa9b95df6b977b40cca6d8713cea up to, but not including, a149dcae23309df9de1c3b6b5d468610ef5ab7de; 17926a79320afa9b95df6b977b40cca6d8713cea up to, but not including, 22f6258e7b31dba9bf88dce4e3ee7f0f20072e60; 17926a79320afa9b95df6b977b40cca6d8713cea up to, but not including, 58fcd1b156152613ba00a064a129fb69507ddd7d; 17926a79320afa9b95df6b977b40cca6d8713cea up to, but not including, fe4447cd95623b1cfacc15f280aab73a6d7340b2; and 1 more ranges252157d939d179b5d767cb860ff8fa7f8723b67a, a75b3b361dd481d942c5f259a82d59718a41092c, b3a808cd0790b5075aaa2bc3588edf02cd71d352, 47073aab8a3a5a7b41c9bd37d2a3dcbeeccd6c8a, a149dcae23309df9de1c3b6b5d468610ef5ab7de, 22f6258e7b31dba9bf88dce4e3ee7f0f20072e60
SiemensSIMATIC S7-1500 TM MFP - GNU/Linux subsystemall versionsNot stated
LinuxLinux Kernel2.6.22.1 up to, but not including, 6.6.135; 6.7 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; 2.6.22; 7.06.6.135, 6.12.82, 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
NetworkCan be exploited remotely over a network, including the internet.
Attack complexity
LowNo special conditions are needed; the attack works reliably.
Privileges required
NoneNo account or login is needed.
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:N/AC:L/PR:N/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: rxrpc: reject undecryptable rxkad response tickets rxkad_decrypt_ticket() decrypts the RXKAD response ticket and then parses the buffer as plaintext without checking whether crypto_skcipher_decrypt() succeeded. A malformed RESPONSE can therefore use a non-block-aligned ticket length, make the decrypt operation fail, and still drive the ticket parser with attacker-controlled bytes. Check the decrypt result and abort the connection with RXKADBADTICKET when ticket decryption fails.

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: yes, 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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