CVE-2026-63940
CRITICAL
Published Jul 19, 2026
Modified Jul 20, 2026
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.
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CVSS v3.1 Score
9.3
CRITICAL
CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H
EPSS — Exploit Prediction
0.0018
Probability of exploitation
0.08%
Percentile rank
EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.
References
Other References
Frequently Asked Questions
What is CVE-2026-63940? +
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. It has a CVSS v3.1 base score of 9.3 (CRITICAL).
How severe is CVE-2026-63940? +
CVE-2026-63940 has a CVSS v3.1 score of 9.3 out of 10, rated CRITICAL. This is a critical vulnerability that should be patched immediately. The EPSS score is 0.0018, placing it in the 0th percentile for exploitation probability.
How do I check if I'm vulnerable to CVE-2026-63940? +
You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.
