What’s Vulnerable › Vulnerabilities

CVE-2026-34516: AIOHTTP: Multipart Header Size Bypass

• Severity: high (CVSS 7.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.4% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-04-01 · updated 2026-10-26
• Weakness: CWE-770

Description

AIOHTTP is an asynchronous HTTP client/server framework for asyncio and Python. Prior to version 3.13.4, a response with an excessive number of multipart headers may be allowed to use more memory than intended, potentially allowing a DoS vulnerability. This issue has been patched in version 3.13.4.

Affected products

• aio-libs aiohttp: before 3.13.4 — fixed in 3.13.4
• Pypi Aiohttp: before 3.13.4; 0.1, 0.10.0, 0.10.1, 0.10.2, 0.11.0, 0.12.0 (+298) — fixed in 3.13.4

How to fix

Upgrade to a fixed version: aio-libs aiohttp 3.13.4; Pypi Aiohttp 3.13.4. Check the vendor advisory for mitigations.

References

• https://github.com/aio-libs/aiohttp/commit/8a74257b3804c9aac0bf644af93070f68f6c5a6f
• https://github.com/aio-libs/aiohttp/releases/tag/v3.13.4
• https://github.com/aio-libs/aiohttp/security/advisories/GHSA-m5qp-6w8w-w647

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