CyberSecBulletin
CVE-2026-63940NVD status: Modified

Linux: Integer Underflow (Wrap or Wraparound)

Published Updated By the CyberSecBulletin desk

CVE-2026-63940 is a critical-severity integer underflow (wrap or wraparound) vulnerability in Linux, with a CVSS 3.1 base score of 9.3 out of 10. It can be exploited with local access to the system by an unauthenticated attacker, without any action from a user. The record lists versions c8aa0a79ab0b23cde4c46ccff78e63be35733e04, bbd3a27e4f99fdcad82d12d79c04a95dff1ff70b, 3b6035bc6bff20e89752ce4358bc4c9a9d5883f2 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 0.21% 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 c8aa0a79ab0b23cde4c46ccff78e63be35733e04 or bbd3a27e4f99fdcad82d12d79c04a95dff1ff70b or 3b6035bc6bff20e89752ce4358bc4c9a9d5883f2 or 2254972d4d69e279ba4e87bf0968eb08ad0d3c92, whichever matches your release line, or a later version.
  2. Update Linux Kernel to 6.6.160 or 6.12.95 or 6.18.35 or 7.0.12, whichever matches your release line, or a later version.

Affected products and versions

VendorProductAffected versionsFixed in
LinuxLinux291bd20d5d88814a73d43b55b9428feab2f28094 up to, but not including, c8aa0a79ab0b23cde4c46ccff78e63be35733e04; 291bd20d5d88814a73d43b55b9428feab2f28094 up to, but not including, bbd3a27e4f99fdcad82d12d79c04a95dff1ff70b; 291bd20d5d88814a73d43b55b9428feab2f28094 up to, but not including, 3b6035bc6bff20e89752ce4358bc4c9a9d5883f2; 291bd20d5d88814a73d43b55b9428feab2f28094 up to, but not including, 2254972d4d69e279ba4e87bf0968eb08ad0d3c92; 291bd20d5d88814a73d43b55b9428feab2f28094 up to, but not including, c30cde934c7813b4e3069765dac64ce3d31e34f2; 291bd20d5d88814a73d43b55b9428feab2f28094 up to, but not including, 3988bd2723de407ae90fa7a6f6029b4e60238c58; 5.11c8aa0a79ab0b23cde4c46ccff78e63be35733e04, bbd3a27e4f99fdcad82d12d79c04a95dff1ff70b, 3b6035bc6bff20e89752ce4358bc4c9a9d5883f2, 2254972d4d69e279ba4e87bf0968eb08ad0d3c92, c30cde934c7813b4e3069765dac64ce3d31e34f2, 3988bd2723de407ae90fa7a6f6029b4e60238c58
LinuxLinux Kernel5.11 up to, but not including, 6.6.160; 6.7 up to, but not including, 6.12.95; 6.13 up to, but not including, 6.18.35; 6.19 up to, but not including, 7.0.12; 7.16.6.160, 6.12.95, 6.18.35, 7.0.12

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
NoneNo account or login is needed.
User interaction
NoneNo action by a victim is required.
Scope
ChangedThe attack can reach beyond the vulnerable component into other systems.
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:N/UI:N/S:C/C:H/I:H/A:H. Scored by CNA.

Official description

In the Linux kernel, the following vulnerability has been resolved: KVM: SEV: Ignore Port I/O requests of length '0' Explicitly ignore Port I/O requests of length '0' (or count '0'), so that setting up the software scratch area (and other code) doesn't have to worry about underflowing the length, and to allow for WARNing on trying to configure the scratch area with len==0.

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

The underlying weakness: Integer Underflow (Wrap or Wraparound)

The product subtracts one value from another, such that the result is less than the minimum allowable integer value, which produces a value that is not equal to the correct result.

More Integer Underflow (Wrap or Wraparound) vulnerabilities (CWE-191)

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 Integer Underflow (Wrap or Wraparound) vulnerabilities

Spotted an error? Tell us.