Bug 2459691 (CVE-2026-31430)

Summary: CVE-2026-31430 kernel: X.509: Fix out-of-bounds access when parsing extensions
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
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Priority: medium    
Version: unspecifiedKeywords: Security
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OS: Linux   
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A flaw was found in the Linux kernel. An unprivileged user can exploit this vulnerability by submitting a specially crafted X.509 certificate to the kernel through the keyrings(7) application programming interface (API). This certificate, specifically when containing empty Basic Constraints or Key Usage extensions, can trigger an out-of-bounds access during parsing. An out-of-bounds access is a memory corruption issue where a program attempts to read or write data beyond the allocated memory region, which can lead to system instability or a denial of service.
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Description OSIDB Bzimport 2026-04-20 11:01:28 UTC 
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.
Comment 1 Keith Grant 2026-04-20 14:38:40 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026042008-CVE-2026-31430-299d@gregkh/T