aiohttp's ClientSession is vulnerable to CRLF injection via method
Summary
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.
Details
The vulnerability occurs only if the attacker can control the HTTP method (GET, POST etc.) of the request.
Previous releases performed no validation on the provided value. If an attacker controls the HTTP method it will be used as is and can lead to HTTP request smuggling.
PoC
A minimal example can be found here: https://gist.github.com/jnovikov/7f411ae9fe6a9a7804cf162a3bdbb44b
Impact
If the attacker can control the HTTP version of the request it will be able to modify the request (request smuggling).
Workaround
If unable to upgrade and using user-provided values for the request method, perform manual validation of the user value (e.g. by restricting it to a few known values like GET, POST etc.).
Affected software
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| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Python (PyPI) | aiohttp | < 3.9.0 | 3.9.0 |
References
- https://github.com/aio-libs/aiohttp/security/advisories/GHSA-qvrw-v9rv-5rjx
- https://gist.github.com/jnovikov/7f411ae9fe6a9a7804cf162a3bdbb44b
- https://github.com/aio-libs/aiohttp/pull/7806/files
- https://github.com/aio-libs/aiohttp/commit/e4ae01c2077d2cfa116aa82e4ff6866857f7c466
- https://nvd.nist.gov/vuln/detail/CVE-2023-49082
- https://github.com/aio-libs/aiohttp
- https://github.com/pypa/advisory-database/tree/main/vulns/aiohttp/PYSEC-2023-251.yaml
- https://lists.debian.org/debian-lts-announce/2025/02/msg00002.html
- https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/TY5SI6NK5243DEEDQUFKQKW5GQNKQUMA
- https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/WSYWMP64ZFCTC3VO6RY6EC6VSSMV6I3A
- CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N- Weakness (CWE)
CWE-20- Platform
- Python (PyPI)
- Package
aiohttp- Disclosed
- 27.11.2023
- Updated
- 11.10.2026 15:17
Sources and licenses
OSV / GitHub Advisory Database - PYSEC-2023-251 - PyPA Advisory Database; CC BY 4.0
OSV / GitHub Advisory Database - GHSA-qvrw-v9rv-5rjx - CC BY 4.0
Vulnerability history: aiohttp
All published vulnerabilities of this package (Python (PyPI)), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 55
- First → latest
- 02.2021 10.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- High 7
- Medium 29
- Low 19
Disclosures per year
- 2021: 1
- 2022: 0
- 2023: 6
- 2024: 7
- 2025: 1
- 2026: 40
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aiohttp's ClientSession is vulnerable to CRLF injection via method this entry
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