AIOHTTP has late size enforcement for non-file multipart fields causes memory DoS
Summary
For some multipart form fields, aiohttp read the entire field into memory before checking client_max_size.
Impact
If an application uses Request.post() an attacker can send a specially crafted multipart request to force significant temporary memory allocation even when the request is ultimately rejected.
Patch: https://github.com/aio-libs/aiohttp/commit/cbb774f38330563422ca0c413a71021d7b944145
Affected software
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| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Python (PyPI) | aiohttp | < 3.13.4 | 3.13.4 |
References
- https://github.com/aio-libs/aiohttp/releases/tag/v3.13.4
- https://github.com/aio-libs/aiohttp/commit/cbb774f38330563422ca0c413a71021d7b944145
- https://github.com/aio-libs/aiohttp/security/advisories/GHSA-3wq7-rqq7-wx6j
- https://nvd.nist.gov/vuln/detail/CVE-2026-34517
- https://github.com/aio-libs/aiohttp
- CVSS vector
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:U- Weakness (CWE)
CWE-770- Platform
- Python (PyPI)
- Package
aiohttp- Disclosed
- 01.04.2026
- Updated
- 11.10.2026 15:17
Sources and licenses
OSV / GitHub Advisory Database - PYSEC-2026-2099 - PyPA Advisory Database; CC BY 4.0
OSV / GitHub Advisory Database - GHSA-3wq7-rqq7-wx6j - 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 has late size enforcement for non-file multipart fields causes memory DoS this entry
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