---
id: CVE-2023-37276
title: aiohttp is an asynchronous HTTP client/server framework for asyncio and Python
summary: >-
  aiohttp is an asynchronous HTTP client/server framework for asyncio and
  Python. aiohttp v3.8.4 and earlier are bundled with llhttp v6.0.6. Vulnerable
  code is used by aiohttp for its HTTP request parser when available which is
  the default…
severity: medium
cvss: 5.3
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N'
cwe:
  - CWE-444
vendor: aiohttp
product: aiohttp
affected:
  - aiohttp <= 3.8.4
published: '2023-07-19'
updated: '2026-06-17'
sourceUpdated: '2026-06-17T06:07:52.237'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2023-37276'
references:
  - url: 'https://github.com/aio-libs/aiohttp/blob/v3.8.4/.gitmodules'
    label: security-advisories@github.com
  - url: >-
      https://github.com/aio-libs/aiohttp/commit/9337fb3f2ab2b5f38d7e98a194bde6f7e3d16c40
    label: security-advisories@github.com
  - url: >-
      https://github.com/aio-libs/aiohttp/security/advisories/GHSA-45c4-8wx5-qw6w
    label: security-advisories@github.com
  - url: 'https://hackerone.com/reports/2001873'
    label: security-advisories@github.com
  - url: 'https://github.com/aio-libs/aiohttp/blob/v3.8.4/.gitmodules'
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: >-
      https://github.com/aio-libs/aiohttp/commit/9337fb3f2ab2b5f38d7e98a194bde6f7e3d16c40
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: >-
      https://github.com/aio-libs/aiohttp/security/advisories/GHSA-45c4-8wx5-qw6w
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: 'https://hackerone.com/reports/2001873'
    label: af854a3a-2127-422b-91ae-364da2661108
tags:
  - nvd
  - cve.org
  - exploit-available
exploitAvailable: true
ssvc:
  exploitation: poc
  automatable: 'yes'
  technicalImpact: partial
  timestamp: '2024-10-18T16:05:51.434153Z'
ingestedAt: '2026-09-13T16:03:50.272Z'
epss: 0.01337
epssPercentile: 0.7004
---

## Overview

aiohttp is an asynchronous HTTP client/server framework for asyncio and Python. aiohttp v3.8.4 and earlier are bundled with llhttp v6.0.6. Vulnerable code is used by aiohttp for its HTTP request parser when available which is the default case when installing from a wheel. This vulnerability only affects users of aiohttp as an HTTP server (ie `aiohttp.Application`), you are not affected by this vulnerability if you are using aiohttp as an HTTP client library (ie `aiohttp.ClientSession`). Sending a crafted HTTP request will cause the server to misinterpret one of the HTTP header values leading to HTTP request smuggling. This issue has been addressed in version 3.8.5. Users are advised to upgrade. Users unable to upgrade can reinstall aiohttp using `AIOHTTP_NO_EXTENSIONS=1` as an environment variable to disable the llhttp HTTP request parser implementation. The pure Python implementation isn't vulnerable.

## Affected

- `aiohttp <= 3.8.4`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.