Inconsistent interpretation of HTTP requests in aiohttp - CVE-2026-34525

Vulnerability identifier: #VU127946

CSH Severity: Low

CVSS v4: 6.3 [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]

CVE-ID: CVE-2026-34525

CWE-ID: CWE-444

Exploitation vector: Remote access

Exploit availability: No public exploit available

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().

aiohttp
SUSE Linux Enterprise Server 15 SP4
SUSE Linux Enterprise Server 15 SP5
SUSE Linux Enterprise Server 15 SP6
SUSE Linux Enterprise High Performance Computing ESPOS 15
SUSE Linux Enterprise Server 15
SUSE Linux Enterprise High Performance Computing LTSS 15
SUSE Linux Enterprise Server for SAP Applications 15
SUSE Linux Enterprise High Performance Computing 15
SUSE Linux Enterprise Desktop 15
SUSE Manager Server
SUSE Manager Retail Branch Server
SUSE Manager Proxy
Public Cloud Module
Python 3 Module
openSUSE Leap
Anolis OS
openEuler
Python for Scientific Computing
Maximo Application Suite - Predict Component
python3-aiohttp-debuginfo
python-aiohttp-debugsource
python3-aiohttp
python311-aiohttp-debuginfo
python311-aiohttp
python3-aiohttp+speedups
python-aiohttp-debuginfo
python-aiohttp-help
python-aiohttp

Install security update from vendor's website.

aiohttp - update to 3.13.4
Python for Scientific Computing - update to 4.3.2
Maximo Application Suite - Predict Component - update to 9.2.1
python3-aiohttp-debuginfo - update to 3.6.0-150100.3.35.1
python-aiohttp-debugsource - addressed in versions 3.6.0-150100.3.35.1, 3.9.3-150400.10.43.1
python3-aiohttp - update to 3.6.0-150100.3.35.1
python311-aiohttp-debuginfo - update to 3.9.3-150400.10.43.1
python311-aiohttp - update to 3.9.3-150400.10.43.1
python3-aiohttp - update to 3.13.3-2
python3-aiohttp+speedups - update to 3.13.3-2
python-aiohttp-debuginfo - update to 3.13.5-1
python3-aiohttp - update to 3.13.5-1
python-aiohttp-help - update to 3.13.5-1
python-aiohttp-debugsource - update to 3.13.5-1
python-aiohttp - update to 3.13.5-1

• https://github.com/aio-libs/aiohttp/security/advisories/GHSA-c427-h43c-vf67
• https://github.com/advisories/GHSA-c427-h43c-vf67

• Multiple vulnerabilities in aiohttp
• openEuler 24.03 LTS update for python-aiohttp
• openEuler 24.03 LTS SP3 update for python-aiohttp
• openEuler 24.03 LTS SP1 update for python-aiohttp
• Anolis OS update for python-aiohttp
• Splunk Python for Scientific Computing update for third-party components
• SUSE update for python-aiohttp
• SUSE update for python-aiohttp
• Multiple vulnerabilities in IBM Maximo Application Suite - Predict Component