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Vulnerability record · CVE-2023-37276 · published 19 July 2023

CVE-2023-37276: Aiohttp http request smuggling vulnerability

Aiohttp · Aiohttp

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.

7.5 CVSS 3.1 High EPSS 1.3% · top 29.9% CWE-444 · HTTP request smuggling
7.5CVSS 3.1 base score
1.3%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
8References, 4 tagged exploit
17 Jun 2026Last modified by NVD

Description

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.

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://github.com/aio-libs/aiohttp/blob/v3.8.4/.gitmodules Product
https://github.com/aio-libs/aiohttp/commit/9337fb3f2ab2b5f38d7e98a194bde6f7e3d16c40 Patch
https://github.com/aio-libs/aiohttp/security/advisories/GHSA-45c4-8wx5-qw6w ExploitMitigationVendor Advisory
https://hackerone.com/reports/2001873 ExploitThird Party Advisory
https://github.com/aio-libs/aiohttp/blob/v3.8.4/.gitmodules Product
https://github.com/aio-libs/aiohttp/commit/9337fb3f2ab2b5f38d7e98a194bde6f7e3d16c40 Patch
https://github.com/aio-libs/aiohttp/security/advisories/GHSA-45c4-8wx5-qw6w ExploitMitigationVendor Advisory
https://hackerone.com/reports/2001873 ExploitThird Party Advisory

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Source: NIST National Vulnerability Database (record CVE-2023-37276), CISA KEV, FIRST EPSS (scores of 2026-09-27). This page is refreshed as NVD updates the record.