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CVE-2025-4565 — protobuf

Fix: protocolbuffers/protobuf@17838be

CVE-2025-4565 is a CWE-674 vulnerability in protobuf. A fix is available for protobuf — see the affected versions and patch details below.

Unbounded recursion in Python Protobuf

Also known asGHSA-8qvm-5x2c-j2w7PYSEC-2026-1806
Published
Updated
Affected
3 pkgs
Patched
3 / 3
Exploits
None indexed
Exploitation data as of Oct 26, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

  • CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
  • CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2025-4565.

EPSS Exploitation Probability

via FIRST.org ↗
0.3%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs17th percentile — riskier than 17% of all scored CVEsHighest risk
0.00%0.26%0.52%0.78%0.0%0.3%Apr 26Aug 26Oct 26

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

3 pkgs affected
🐍protobuf🐍protobuf🐍protobuf

Real-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

Summary

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.

Reporter: Alexis Challande, Trail of Bits Ecosystem Security Team [email protected]

Affected versions: This issue only affects the pure-Python implementation of protobuf-python backend. This is the implementation when PROTOCOL_BUFFERS_PYTHON_IMPLEMENTATION=python environment variable is set or the default when protobuf is used from Bazel or pure-Python PyPi wheels. CPython PyPi wheels do not use pure-Python by default.

This is a Python variant of a previous issue affecting protobuf-java.

Severity

This is a potential Denial of Service. Parsing nested protobuf data creates unbounded recursions that can be abused by an attacker.

Proof of Concept

For reproduction details, please refer to the unit tests decoder_test.py and message_test

Remediation and Mitigation

A mitigation is available now. Please update to the latest available versions of the following packages:

  • protobuf-python(4.25.8, 5.29.5, 6.31.1)

Affected Packages

3 total 3 fixed
EcosystemPackageVulnerable rangeFix
🐍PyPIprotobufall versions4.25.8pip install --upgrade 'protobuf==4.25.8'
🐍PyPIprotobuf≥ 5.26.0rc1&&< 5.29.55.29.5pip install --upgrade 'protobuf==5.29.5'
🐍PyPIprotobuf≥ 6.30.0rc1&&< 6.31.16.31.1pip install --upgrade 'protobuf==6.31.1'

Affected Products

1 product · 3 configurations
Application
protobuf-pythongoogle
≥ 6.30.0 && < 6.31.1
range

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for protobuf, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. 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.

  3. Workarounds

    Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatModerate

The availability impact of this denial-of-service vulnerability is confined to applications that directly integrate the Protobuf package. Within the context of a Red Hat system, the host machine itself is not expected to be impacted, thereby limiting the scope of disruption to individual application instances rather…

Workaround published by Red Hat
Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability.
Source: Red Hat security advisory for CVE-2025-4565 (CC BY 4.0)
ProductFixed inAdvisory
Red Hat Ansible Automation Platform 2.6 for RHEL 9python3.11-protobuf-0:4.25.8-1.el9apRHSA-2026:1249
Red Hat OpenShift Container Platform 4.19openshift4/ose-dpu-intel-ipu-vsp-rhel9:v4.19.0-202507081507.p0.gb4d5e23.assembly.stream.el9RHSA-2025:10773
Red Hat Ansible Automation Platform 2.6ansible-automation-platform-26/gateway-rhel9:1772543959RHSA-2026:3960

Frequently Asked Questions

### Summary 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`](https://protobuf.dev/programming-guides/encoding/#groups) tags** can be corrupted by exceeding the Python recursion limit. Reporter: Alexis Challande, Trail of Bits Ecosystem Security Team [[email protected]](mailto:[email protected]) Affected versions: This issue only affects the [pure-Python implementation](https://github.com/protocolbuffers/protobuf/tree/main/python
O3 Security · Impact-Aware SCA

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CVE-2025-4565: protobuf DoS — Fixed in 4.25.8