# CVE-2026-128131: AIOHTTP: Concatenated compressed streams cause excessive CPU use

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, aiohttp decompresses each member of a payload containing many concatenated gzip, deflate, or zstd streams by passing the entire remaining input to a new decompressor, causing quadratic CPU use. Empty members produce no output, so client_max_size and output backpressure do not limit the work. A remote attacker can block a server event loop with a crafted compressed request body or WebSocket message, and a malicious server can similarly block a client. 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, CWE-407

## 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-h4cc-hm5h-fmm9 (CNA: GitHub_M; x_refsource_CONFIRM)

- https://github.com/aio-libs/aiohttp/pull/13362 (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/aio-libs/aiohttp/pull/13391 (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/aio-libs/aiohttp/commit/d041d4d0fd48c3f0832084d33be16cf1c4835f85 (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/aio-libs/aiohttp/commit/d925a80539ffd227da1d93ab4a5bff123cc777db (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-2026-128131; retrieved 2026-11-13; source updated 2026-11-13

Revision: 98c71387886804768f69d4ea9788e223a037308fe7f423aecea4a0be4f67fa58

Canonical: https://y2.dev/cve/CVE-2026-128131

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