Inconsistent interpretation of HTTP requests in aiohttp - CVE-2026-34525
Published: April 26, 2026
Vulnerability identifier: #VU127946
CSH Severity: Low
CVSS v4.0: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:U/U:Clear
CVE-ID: CVE-2026-34525
CWE-ID: CWE-444
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vendor: aio-libs
Affected software:
aiohttp
aiohttp
Detailed vulnerability description
The vulnerability allows a remote attacker to bypass a security check and access a privileged sub application.
The vulnerability exists due to inconsistent interpretation of HTTP requests in Host header handling when processing requests with multiple Host headers through a reverse proxy. A remote attacker can send a specially crafted request with duplicate Host headers to bypass a security check and access a privileged sub application.
Exploitation is theoretically possible when a reverse proxy applies security rules based on the target Host and the application uses Application.add_domain().
How to mitigate CVE-2026-34525
Install security update from vendor's website.