aiohttp vulnerable to Denial of Service when trying to parse malformed POST requests
Summary
An attacker can send a specially crafted POST (multipart/form-data) request. When the aiohttp server processes it, the server will enter an infinite loop and be unable to process any further requests.
Impact
An attacker can stop the application from serving requests after sending a single request.
For anyone needing to patch older versions of aiohttp, the minimum diff needed to resolve the issue is (located in _read_chunk_from_length()):
diff --git a/aiohttp/multipart.py b/aiohttp/multipart.py
index 227be605c..71fc2654a 100644
--- a/aiohttp/multipart.py
+++ b/aiohttp/multipart.py
@@ -338,6 +338,8 @@ class BodyPartReader:
assert self._length is not None, "Content-Length required for chunked read"
chunk_size = min(size, self._length - self._read_bytes)
chunk = await self._content.read(chunk_size)
+ if self._content.at_eof():
+ self._at_eof = True
return chunk
async def _read_chunk_from_stream(self, size: int) -> bytes:This does however introduce some very minor issues with handling form data. So, if possible, it would be recommended to also backport the changes in: https://github.com/aio-libs/aiohttp/commit/cebe526b9c34dc3a3da9140409db63014bc4cf19 https://github.com/aio-libs/aiohttp/commit/7eecdff163ccf029fbb1ddc9de4169d4aaeb6597 https://github.com/aio-libs/aiohttp/commit/f21c6f2ca512a026ce7f0f6c6311f62d6a638866
Affected software
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| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Python (PyPI) | aiohttp | < 3.9.4 | 3.9.4 |
References
- https://github.com/aio-libs/aiohttp/security/advisories/GHSA-5m98-qgg9-wh84
- https://nvd.nist.gov/vuln/detail/CVE-2024-30251
- https://github.com/aio-libs/aiohttp/commit/7eecdff163ccf029fbb1ddc9de4169d4aaeb6597
- https://github.com/aio-libs/aiohttp/commit/cebe526b9c34dc3a3da9140409db63014bc4cf19
- https://github.com/aio-libs/aiohttp/commit/f21c6f2ca512a026ce7f0f6c6311f62d6a638866
- https://github.com/aio-libs/aiohttp
- https://lists.debian.org/debian-lts-announce/2025/02/msg00002.html
- http://www.openwall.com/lists/oss-security/2024/05/02/4
- https://pypi.org/project/aiohttp
- https://github.com/advisories/GHSA-5m98-qgg9-wh84
- CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H- Weakness (CWE)
CWE-835- Platform
- Python (PyPI)
- Package
aiohttp- Disclosed
- 03.05.2024
- Updated
- 11.10.2026 15:17
Sources and licenses
OSV / GitHub Advisory Database - PYSEC-2026-1098 - PyPA Advisory Database; CC BY 4.0
OSV / GitHub Advisory Database - GHSA-5m98-qgg9-wh84 - 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
-
aiohttp vulnerable to Denial of Service when trying to parse malformed POST requests this entry
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