What is CVE-2023-37276?

CVE-2023-37276 is a medium-severity vulnerability in Aiohttp, classified under Inconsistent Interpretation of HTTP Requests (HTTP Request/Response Smuggling). CVSS score: 5.3/10. Published 2023-07-19.

How severe is CVE-2023-37276?

Medium severity. CVSS v3 base score is 5.3 out of 10.

Vulnerability in Aiohttp

CVE-2023-37276

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.

Vulnerability class: HTTP Request Smuggling

Published 2023-07-19 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 5.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N.

EPSS exploit prediction

EPSS: 0.013 (70.1th percentile), scored 2026-09-29.

Low probability of exploitation in the next 30 days, but still tracked. 70th percentile — 70.1% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.013 · newest: 0.013 · change: 0.000

Affected products

Aiohttp
Aio-Libs Aiohttp — versions < 3.8.5

Weakness classification (CWE)

CWE-444 — Inconsistent Interpretation of HTTP Requests (HTTP Request/Response Smuggling)

References

github.com/aio-libs/aiohttp/security/advisories/GHSA-45c4-8wx5-qw6w (Exploit, Mitigation, Vendor Advisory)
github.com/aio-libs/aiohttp/commit/9337fb3f2ab2b5f38d7e98a194bde6f7e3d16c40 (Patch)
hackerone.com/reports/2001873 (Exploit, Third Party Advisory)
github.com/aio-libs/aiohttp/blob/v3.8.4/.gitmodules (Product)

Frequently asked questions

What is CVE-2023-37276?: CVE-2023-37276 is a medium-severity vulnerability in Aiohttp, classified under Inconsistent Interpretation of HTTP Requests (HTTP Request/Response Smuggling). CVSS score: 5.3/10. Published 2023-07-19.
How severe is CVE-2023-37276?: Medium severity. CVSS v3 base score is 5.3 out of 10.