CVE-2026-31430: X.509: Fix out-of-bounds access when parsing extensions

Severity: high (CVSS 7.1 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.1% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-04-20 · updated 2026-06-17
Weakness: CWE-125

Description

In the Linux kernel, the following vulnerability has been resolved: X.509: Fix out-of-bounds access when parsing extensions Leo reports an out-of-bounds access when parsing a certificate with empty Basic Constraints or Key Usage extension because the first byte of the extension is read before checking its length. Fix it. The bug can be triggered by an unprivileged user by submitting a specially crafted certificate to the kernel through the keyrings(7) API. Leo has demonstrated this with a proof-of-concept program responsibly disclosed off-list.

Affected products

Linux kernel: from 6.4 before 6.6.135; from 6.7 before 6.12.82; from 6.13 before 6.18.23; from 6.19 before 6.19.13; 7.0-rc1, 7.0-rc2, 7.0-rc3, 7.0-rc4, 7.0-rc5, 7.0-rc6 (+1) — fixed in 6.12.82, 6.18.23, 6.19.13, 6.6.135

How to fix

Upgrade to a fixed version: Linux kernel 6.12.82, 6.18.23, 6.19.13, 6.6.135. Check the vendor advisory for mitigations.

References

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