Vulnerability · Published Apr 16, 2026 · Assigned by Google
CVE-2026-6409Denial of Service (DoS) vulnerability exists in the Protobuf PHP library during the parsing of untrusted input
High 7.1
In plain English
A high-severity improper input validation in Protobuf-php (Pecl) from Protocol Buffers. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 30% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
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 packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | protobuf | 3.21.12-3+deb12u1 | DEBIAN-CVE-2026-6409 |
| Debian:13 | protobuf | 3.21.12-11+deb13u1 | DEBIAN-CVE-2026-6409 |
| Debian:14 | protobuf | 3.21.12-16 | DEBIAN-CVE-2026-6409 |
| Packagist | google/protobuf | 4.33.6 | GHSA-p2gh-cfq4-4wjc |
| Ubuntu:24.04:LTS | protobuf | no fix listed | UBUNTU-CVE-2026-6409 |
| Ubuntu:24.04:LTS | protobuf | 3.21.12-8.2ubuntu0.4 | USN-8943-1 |
| Ubuntu:25.10 | protobuf | no fix listed | UBUNTU-CVE-2026-6409 |
| Ubuntu:26.04:LTS | protobuf | 3.21.12-15ubuntu1.1 | USN-8943-1 |
| Ubuntu:26.04:LTS | protobuf | no fix listed | UBUNTU-CVE-2026-6409 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| Protocol Buffers | Protobuf-php (Pecl) | 0 – before 5.34.0-RC10 – before 4.33.6 |
Weakness: CWE-20 · Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N