CVE-2026-6409

Denial of Service (DoS) vulnerability exists in the Protobuf PHP library during the parsing of untrusted input

CVE-2026-6409 is fixed in protobuf on 1 platform, first by DEBIAN-CVE-2026-6409, released April 16, 2026. It is not reported as exploited. Patch Radar priority: High.

High

CVSS

n/a

Important

Exploitation

None reported

No vendor assessment

CISA KEV

Not listed

Not in the Known Exploited Vulnerabilities catalog

EPSS

0.0036

29th percentile

A Denial of Service (DoS) vulnerability exists in the Protobuf PHP library during the parsing of untrusted input. Maliciously structured messages—specifically those containing negative varints or deep recursion—can be used to crash the application, impacting service availability.

Where it's fixed

Product	Fixed in	Fix	Released
Linux
protobuf · Debian 12.15 (bookworm)	3.21.12-3+deb12u1	DEBIAN-CVE-2026-6409	Apr 16, 2026
protobuf · Debian 13.5 (trixie)	3.21.12-11+deb13u1	DEBIAN-CVE-2026-6409	Apr 16, 2026
protobuf · Debian 14	3.21.12-16	DEBIAN-CVE-2026-6409	Apr 16, 2026

Details

Published
April 16, 2026
Weakness
Improper Input Validation
Vendor advisory
https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-6409

For tools and AI agents

This page as data: JSON · Markdown

Link to this page

If this page saved you time, a link to it in your ticket, advisory or write-up helps others find it.

HTML

<a href="https://patchblox.com/security/cve/CVE-2026-6409">CVE-2026-6409 on Patchblox Patch Radar</a>

Reusing the data? How to credit Patch Radar.

Is this on your machines?

Patchblox finds every install below the fixed version on Windows, macOS and Linux, and updates them through your release rings.

Get a demo

Patch Radar data is free to use with attribution. Terms and how to credit it.

Product names, logos and trademarks shown on Patch Radar belong to their respective owners. They are used only to identify the software each security fix applies to and to help readers find their platform. Their use does not imply any affiliation with, or endorsement by, those owners, and Patchblox is not affiliated with any of them.