# CVE-2026-128127: AIOHTTP: Base64 multipart parts bypass client_max_size

Status: published. Published: 2026-11-13. Updated: 2026-11-13.

AIOHTTP is an asynchronous HTTP client/server framework for asyncio and Python. Prior to 3.14.4, BodyPartReader.read_chunk() processing a multipart part with Content-Transfer-Encoding set to base64 keeps reading until the chunk length is a multiple of four without enforcing a byte limit. A short Content-Length or a long run of whitespace can cause one call to read the remaining body into memory before the size check or spin on the event loop. A remote attacker can send such a multipart request to a handler that reads multipart data and bypass client_max_size. This issue is fixed in version 3.14.4.

## Remediation

No remediation reported in collected sources

## Affected products and versions

- aio-libs / aiohttp: < 3.14.4 (affected). Source: CNA: GitHub_M

## Severity and prioritization

- CVSS 4.0: 8.7 (high); CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N; source: CNA: GitHub_M

- CISA KEV: No listing in collected sources

- EPSS: Not available

- SSVC: Not available

- Weaknesses: CWE-400

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://github.com/aio-libs/aiohttp/security/advisories/GHSA-24c4-3p7v-29cm (CNA: GitHub_M; x_refsource_CONFIRM)

- https://github.com/aio-libs/aiohttp/pull/13509 (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/aio-libs/aiohttp/pull/13513 (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/aio-libs/aiohttp/commit/2d9c5c1062eff0034fb3ab120897a6c1b3ff7041 (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/aio-libs/aiohttp/commit/a555ab698e08e9baea7386d5b4c0761cb8956fdd (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/aio-libs/aiohttp/releases/tag/v3.14.4 (CNA: GitHub_M; x_refsource_MISC)

## Provenance

- CNA: GitHub_M: https://www.cve.org/CVERecord?id=CVE-2026-128127; retrieved 2026-11-13; source updated 2026-11-13

Revision: 1483aaa6c02d8c485107ba504eae8df540d2ae8788d6a3ae4ca05bbfe32c2270

Canonical: https://y2.dev/cve/CVE-2026-128127

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