CVE-2025-4565
CVE-2025-4565 is a CWE-674 vulnerability in protobuf. O3 Security confirms whether CVE-2025-4565 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Unbounded recursion in Python Protobuf
Blast Radius
protobuf🐍protobuf🐍protobufReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.
Description
Any project that uses Protobuf Pure-Python backend to parse untrusted Protocol Buffers data containing an arbitrary number of recursive groups, recursive messages or a series of SGROUP tags can be corrupted by exceeding the Python recursion limit. This can result in a Denial of service by crashing the application with a RecursionError. We recommend upgrading to version =>6.31.1 or beyond commit 17838beda2943d08b8a9d4df5b68f5f04f26d901
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | protobuf | all versions | 4.25.8 |
| 🐍PyPI | protobuf | ≥ 5.26.0rc1&&< 5.29.5 | 5.29.5 |
| 🐍PyPI | protobuf | ≥ 6.30.0rc1&&< 6.31.1 | 6.31.1 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for 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 protobuf to 4.25.8 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2025-4565 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-2025-4565 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-2025-4565. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2025-4565 in your dependencies?
O3 detects CVE-2025-4565 across PyPI dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.