---
id: CVE-2026-34519
aliases:
  - GHSA-mwh4-6h8g-pg8w
  - PYSEC-2026-2101
title: AIOHTTP has HTTP response splitting via \r in reason phrase
summary: AIOHTTP has HTTP response splitting via \r in reason phrase
severity: low
vendor: aiohttp
product: aiohttp
ecosystem: pip
affected:
  - aiohttp < 3.13.4
patched:
  - aiohttp 3.13.4
published: '2026-04-01'
updated: '2026-09-10'
sourceUpdated: '2026-09-10T03:50:44.819886754Z'
source: OSV
sourceUrl: 'https://osv.dev/vulnerability/GHSA-mwh4-6h8g-pg8w'
references:
  - url: >-
      https://github.com/aio-libs/aiohttp/security/advisories/GHSA-mwh4-6h8g-pg8w
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-34519'
  - url: >-
      https://github.com/aio-libs/aiohttp/commit/53b35a2f8869c37a133e60bf1a82a1c01642ba2b
  - url: 'https://github.com/aio-libs/aiohttp'
  - url: 'https://github.com/aio-libs/aiohttp/releases/tag/v3.13.4'
tags:
  - osv
  - pip
epss: 0.00398
epssPercentile: 0.31296
ingestedAt: '2026-07-13T18:58:00.931Z'
---

## Overview

### Summary

An attacker who controls the `reason` parameter when creating a `Response` may be able to inject extra headers or similar exploits.

### Impact

In the unlikely situation that an application allows untrusted data to be used in the response's `reason` parameter, then an attacker could manipulate the response to send something different from what the developer intended.

-----

Patch: https://github.com/aio-libs/aiohttp/commit/53b35a2f8869c37a133e60bf1a82a1c01642ba2b

## Affected packages

- `aiohttp < 3.13.4`

## Remediation

Upgrade to a patched release:

- `aiohttp 3.13.4`