GHSA-c427-h43c-vf67 — medium GitHub Advisory (CVE-2026-34525) in pip/aiohttp

Description

Summary

Multiple Host headers were allowed in aiohttp.

Impact

Mostly this doesn't affect aiohttp security itself, but if a reverse proxy is applying security rules depending on the target Host, it is theoretically possible that the proxy and aiohttp could process different host names, possibly resulting in bypassing a security check on the proxy and getting a request processed by aiohttp in a privileged sub app when using Application.add_domain().

Patch: https://github.com/aio-libs/aiohttp/commit/e00ca3cca92c465c7913c4beb763a72da9ed8349
Patch: https://github.com/aio-libs/aiohttp/commit/53e2e6fc58b89c6185be7820bd2c9f40216b3000

Basic information

Type: reviewed
Severity: medium
Advisory on GitHub: Open advisory ↗
Repository advisory: Open repository advisory ↗
Source code: Browse source ↗
Published (advisory): 2026-04-01 21:49:45 UTC
Updated: 2026-04-01 21:49:46 UTC
GitHub reviewed: 2026-04-01 21:49:45 UTC
NVD published: 2026-04-01

Score	Percentile
0.12%	30.90%

CVSS Scores

Base score	Version	Severity	Vector
6.3	4.0	—	`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` Click to expand Attack vector (AV:N) Could be attacked over the internet or any normal routed network. Attack complexity (AC:H) Exploitation depends on constrained or hard-to-reproduce conditions. Attack requirements (AT:P) Additional preconditions must be present for exploitation. Privileges required (PR:N) No privileges are required. User interaction (UI:N) No user interaction is required. Vulnerable system confidentiality impact (VC:N) No confidentiality impact on the vulnerable system. Vulnerable system integrity impact (VI:L) Limited integrity impact on the vulnerable system. Vulnerable system availability impact (VA:N) No availability impact on the vulnerable system. Subsequent system confidentiality impact (SC:L) Limited confidentiality impact on subsequent systems. Subsequent system integrity impact (SI:L) Limited integrity impact on subsequent systems. Subsequent system availability impact (SA:N) No availability impact on subsequent systems.

Identifiers

Type	Value
GHSA	GHSA-c427-h43c-vf67 ↗
CVE	CVE-2026-34525 ↗

CWEs

CWE id	Name
CWE-20	Improper Input Validation
CWE-444	Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')

Credits

5yu4n (reporter)
rodrigobnogueira (remediation_developer)
bdraco (remediation_developer)

Affected packages (1)

Vulnerable version ranges and first patched releases as published by GitHub.

Ecosystem	Package	Vulnerable range	First patched	Vulnerable functions
pip	aiohttp	<= 3.13.3	3.13.4	—

AIOHTTP accepts duplicate Host headers