HTTP response splitting in aiohttp - CVE-2026-34520

Vulnerability identifier: #VU127947

CSH Severity: Medium

CVSS v4: 6.9 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N]

CVE-ID: CVE-2026-34520

CWE-ID: CWE-113

Exploitation vector: Remote access

Exploit availability: No public exploit available

The vulnerability allows a remote attacker to bypass security controls.

The vulnerability exists due to improper neutralization of control characters in HTTP response headers in the C parser (llhttp) when processing response header values. A remote attacker can send specially crafted header values to bypass security controls.

The issue can cause header values to be interpreted differently than expected by application logic or intermediary components such as reverse proxies.

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-63hf-3vf5-4wqf
• https://github.com/advisories/GHSA-63hf-3vf5-4wqf

• 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