How severe is CVE-2026-6409?

No CVSS score has been assigned to CVE-2026-6409 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2026-6409?

CVE-2026-6409 affects the following packages: google/protobuf (Packagist). Ecosystems affected: Packagist.

How do I fix CVE-2026-6409?

Update google/protobuf to 4.33.6 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-6409 is resolved across your whole dependency graph.

How do I detect CVE-2026-6409 in my Packagist dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for google/protobuf. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.

How do I mitigate CVE-2026-6409 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

How does O3 Security protect against CVE-2026-6409?

O3 pinpoints whether CVE-2026-6409 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.

Is CVE-2026-6409 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-6409 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What type of vulnerability is CVE-2026-6409?

CVE-2026-6409 is classified as Improper Input Validation (CWE-20). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-6409 published, and has it been updated?

CVE-2026-6409 was published on April 16, 2026 and was last updated on July 17, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐘 Packagist

CVE-2026-6409

CVE-2026-6409 is a Improper Input Validation vulnerability in google/protobuf. O3 Security confirms whether CVE-2026-6409 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.

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

Also known asGHSA-p2gh-cfq4-4wjc

Published

Apr 16, 2026

Updated

Jul 17, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Blast Radius

1 pkg affected

🐘google/protobuf

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Packagist packages — download data is not available via public APIs for these ecosystems.

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

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐘Packagist	`google/protobuf`	all versions	4.33.6

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for google/protobuf. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update google/protobuf to 4.33.6 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-6409 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether CVE-2026-6409 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.

Tailored to CVE-2026-6409. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.

Frequently Asked Questions

O3 Security · Impact-Aware SCA

Is CVE-2026-6409 in your dependencies?

O3 detects CVE-2026-6409 across Packagist dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.

Scan my dependencies How O3 SCA works