aiohttp vulnerable to Denial of Service when trying to parse malformed POST requests

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

7.5 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS

• CVE-2024-30251: 1.09% estimated exploitation activity in the next 30 days; percentile 65.55 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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 readchunkfromlength()): 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

Published by the source

3 May 2024, 17:29 UTC

Last modified by the source

10 Sep 2026, 03:50 UTC

Source last checked

26 Oct 2026, 13:35 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-5m98-qgg9-wh84

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-5m98-qgg9-wh84

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# Patch Next advisory brief: CVE-2024-30251

Advisory: aiohttp vulnerable to Denial of Service when trying to parse malformed POST requests
IDs: CVE-2024-30251, GHSA-5m98-qgg9-wh84
Record: https://patchnext.com/advisories/cve-2024-30251 (revision 2, source checked 26 Oct 2026, 13:35 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: aiohttp 3.9.4. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI aiohttp: affected < 3.9.4; fixed in 3.9.4

## Suggested inspection (read-only)
- `python -m pip show aiohttp`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on aiohttp.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-5m98-qgg9-wh84 (OSV record GHSA-5m98-qgg9-wh84 lists affected ranges: PyPI aiohttp >=0 <3.9.4 (fixed))
- Verified: https://github.com/advisories/GHSA-5m98-qgg9-wh84 (GitHub-reviewed advisory GHSA-5m98-qgg9-wh84 lists affected ranges: PyPI aiohttp >=0 <3.9.4)

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