CVE intelligence and bounded remediation

CVE-2026-34525 — AIOHTTP is an asynchronous HTTP client/server framework for asyncio and Python

Medium CVSS 6.3

AIOHTTP is an asynchronous HTTP client/server framework for asyncio and Python. Prior to version 3.13.4, multiple Host headers were allowed in aiohttp. This issue has been patched in version 3.13.4.

Severity
Medium
CVSS
6.3 (4.0)
Published
2026-04-01
CISA KEV
Not currently listed
Ecosystem
python/pypi
Weaknesses
CWE-20, CWE-444

Affected products

  • aiohttp / aiohttp

Matched remediation archetype

HTTP request smuggling and message-boundary ambiguity

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Check exposure

  • Inventory every proxy, CDN, gateway, load balancer, service mesh, and application server hop on affected request paths.
  • Compare documented parsing and normalization behavior for message length, transfer coding, duplicate headers, and protocol translation.
  • Identify connection reuse and which downstream services trust headers added by intermediaries.

Remediate safely

  • Update affected intermediaries and origin servers and align them on a single standards-compliant request framing policy.
  • Reject ambiguous length, transfer-coding, duplicate, malformed, and unsupported framing before forwarding.
  • Normalize or remove hop-by-hop and identity headers at one controlled boundary and add multi-hop regression tests.

Authoritative sources

Complete CVE record and remediation plan

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