aiohttp's ClientSession is vulnerable to CRLF injection via version
Summary
Improper validation make it possible for an attacker to modify the HTTP request (e.g. to insert a new header) or even create a new HTTP request if the attacker controls the HTTP version.
Details
The vulnerability only occurs if the attacker can control the HTTP version of the request (including its type).
For example if an unvalidated JSON value is used as a version and the attacker is then able to pass an array as the version parameter.
Furthermore, the vulnerability only occurs when the Connection header is passed to the headers parameter.
At this point, the library will use the parsed value to create the request. If a list is passed, then it bypasses validation and it is possible to perform CRLF injection.
PoC
The POC below shows an example of providing an unvalidated array as a version: https://gist.github.com/jnovikov/184afb593d9c2114d77f508e0ccd508e
Impact
CRLF injection leading to Request Smuggling.
Workaround
If these specific conditions are met and you are unable to upgrade, then validate the user input to the version parameter to ensure it is a str.
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-q3qx-c6g2-7pw2
- https://gist.github.com/jnovikov/184afb593d9c2114d77f508e0ccd508e
- https://github.com/aio-libs/aiohttp/pull/7835/files
- https://github.com/aio-libs/aiohttp/commit/1e86b777e61cf4eefc7d92fa57fa19dcc676013b
- https://nvd.nist.gov/vuln/detail/CVE-2023-49081
- https://github.com/aio-libs/aiohttp
- https://github.com/pypa/advisory-database/tree/main/vulns/aiohttp/PYSEC-2023-250.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:C/C:L/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-2023-250 - PyPA Advisory Database; CC BY 4.0
OSV / GitHub Advisory Database - GHSA-q3qx-c6g2-7pw2 - 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 version this entry
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