Vulnerability · Published Apr 1, 2026 · Assigned by GitHub_M
CVE-2026-34525AIOHTTP: Duplicate Host header accepted
Medium 6.3
In plain English
A medium-severity improper input validation in aiohttp from aio-libs. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 23% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Severity (CVSS 4.0)6.3Medium
Exploit odds (30 days)0.3%top 77.3% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known
Official description
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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Alpine:v3.23 | py3-aiohttp | 3.13.5-r0 | ALPINE-CVE-2026-34525 |
| Alpine:v3.24 | py3-aiohttp | 3.13.5-r0 | ALPINE-CVE-2026-34525 |
| Debian:12 | python-aiohttp | 3.8.4-1+deb12u2 | DEBIAN-CVE-2026-34525 |
| Debian:13 | python-aiohttp | no fix listed | DEBIAN-CVE-2026-34525 |
| Debian:14 | python-aiohttp | 3.13.5-1 | DEBIAN-CVE-2026-34525 |
| PyPI | aiohttp | 3.13.4 | PYSEC-2026-2103 |
| PyPI | aiohttp | 3.13.4 | GHSA-c427-h43c-vf67 |
| Ubuntu:25.10 | python-aiohttp | no fix listed | UBUNTU-CVE-2026-34525 |
| Ubuntu:26.10 | python-aiohttp | no fix listed | UBUNTU-CVE-2026-34525 |
Affected products (as reported)
Weakness: CWE-20, CWE-444 · Vector: CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:L/SI:L/SA:N
References
- https://github.com/aio-libs/aiohttp/security/advisories/GHSA-c427-h43c-vf67 x_refsource_CONFIRM
- https://github.com/aio-libs/aiohttp/commit/53e2e6fc58b89c6185be7820bd2c9f40216b3000 x_refsource_MISC
- https://github.com/aio-libs/aiohttp/commit/e00ca3cca92c465c7913c4beb763a72da9ed8349 x_refsource_MISC
- https://github.com/aio-libs/aiohttp/releases/tag/v3.13.4 x_refsource_MISC