---
id: CVE-2025-4565
aliases:
  - GHSA-8qvm-5x2c-j2w7
  - PYSEC-2026-1806
title: protobuf-python has a potential Denial of Service issue
summary: protobuf-python has a potential Denial of Service issue
severity: high
vendor: protobuf
product: protobuf
ecosystem: pip
affected:
  - protobuf < 4.25.8
  - 'protobuf >= 5.26.0rc1, < 5.29.5'
  - 'protobuf >= 6.30.0rc1, < 6.31.1'
patched:
  - protobuf 4.25.8
  - protobuf 5.29.5
  - protobuf 6.31.1
published: '2025-06-16'
updated: '2026-09-10'
sourceUpdated: '2026-09-10T03:50:25.255076549Z'
source: OSV
sourceUrl: 'https://osv.dev/vulnerability/GHSA-8qvm-5x2c-j2w7'
references:
  - url: >-
      https://github.com/protocolbuffers/protobuf/security/advisories/GHSA-735f-pc8j-v9w8
  - url: >-
      https://github.com/protocolbuffers/protobuf/security/advisories/GHSA-8qvm-5x2c-j2w7
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2025-4565'
  - url: >-
      https://github.com/protocolbuffers/protobuf/commit/17838beda2943d08b8a9d4df5b68f5f04f26d901
  - url: 'https://github.com/protocolbuffers/protobuf'
  - url: >-
      https://github.com/protocolbuffers/protobuf/blob/main/python/google/protobuf/internal/decoder_test.py#L87-L98
  - url: >-
      https://github.com/protocolbuffers/protobuf/blob/main/python/google/protobuf/internal/message_test.py#L1436-L1478
  - url: >-
      https://github.com/protocolbuffers/protobuf/tree/main/python#implementation-backends
tags:
  - osv
  - pip
epss: 0.00255
epssPercentile: 0.17426
ingestedAt: '2026-07-08T18:25:47.537Z'
---

## Overview

### 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
[ecosystem@trailofbits.com](mailto:ecosystem@trailofbits.com)

Affected versions: This issue only affects the [pure-Python implementation](https://github.com/protocolbuffers/protobuf/tree/main/python#implementation-backends) 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](https://github.com/protocolbuffers/protobuf/security/advisories/GHSA-735f-pc8j-v9w8).

### 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](https://github.com/protocolbuffers/protobuf/blob/main/python/google/protobuf/internal/decoder_test.py#L87-L98) and [message_test](https://github.com/protocolbuffers/protobuf/blob/main/python/google/protobuf/internal/message_test.py#L1436-L1478)

### 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

- `protobuf < 4.25.8`
- `protobuf >= 5.26.0rc1, < 5.29.5`
- `protobuf >= 6.30.0rc1, < 6.31.1`

## Remediation

Upgrade to a patched release:

- `protobuf 4.25.8`
- `protobuf 5.29.5`
- `protobuf 6.31.1`