CVE-2026-6409: Protocol Buffers Protobuf-PHP Pecl

High severity, CVSS 7.1. EPSS: 0.4% chance of exploitation in the next 30 days.

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.

Affected products

• Protocol Buffers Protobuf-PHP Pecl: before 5.34.0-RC1 (fixed in 5.34.0-RC1); before 4.33.6 (fixed in 4.33.6)

Published 2026-04-16. Last modified 2026-06-17.