AIOHTTP Affected by Denial of Service (DoS) via Unbounded DNS Cache in TCPConnector

Exploitation

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

CVSS 4.0

2.7 · 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 · score source

EPSS

• CVE-2026-34513: 0.46% estimated exploitation activity in the next 30 days; percentile 39.71 (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 unbounded DNS cache could result in excessive memory usage possibly resulting in a DoS situation. Impact If an application makes requests to a very large number of hosts, this could cause the DNS cache to continue growing and slowly use excessive amounts of memory. ----- Patch: https://github.com/aio-libs/aiohttp/commit/c4d77c3533122be353b8afca8e8675e3b4cbda98

Published by the source

1 Apr 2026, 21:19 UTC

Last modified by the source

10 Sep 2026, 03:51 UTC

Source last checked

26 Oct 2026, 13:40 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-hcc4-c3v8-rx92

2. Revision 2 · amended · 25 Oct 2026

   Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

3. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-hcc4-c3v8-rx92

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# Patch Next advisory brief: CVE-2026-34513

Advisory: AIOHTTP Affected by Denial of Service (DoS) via Unbounded DNS Cache in TCPConnector
IDs: CVE-2026-34513, GHSA-hcc4-c3v8-rx92
Record: https://patchnext.com/advisories/cve-2026-34513 (revision 3, source checked 26 Oct 2026, 13:40 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Low (CVSS 2.7)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: aiohttp 3.13.4. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI aiohttp: affected <= 3.13.3; fixed in 3.13.4

## 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-hcc4-c3v8-rx92 (OSV record GHSA-hcc4-c3v8-rx92 lists affected ranges: PyPI aiohttp >=0 <3.13.4 (fixed))
- Verified: https://github.com/advisories/GHSA-hcc4-c3v8-rx92 (GitHub-reviewed advisory GHSA-hcc4-c3v8-rx92 lists affected ranges: PyPI aiohttp >=0 <=3.13.3)

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