HTTP response splitting in aiohttp - CVE-2026-34519
Published: April 26, 2026
Vulnerability identifier: #VU127948
CSH Severity: Medium
CVSS v4.0: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N/E:U/U:Green
CVE-ID: CVE-2026-34519
CWE-ID: CWE-113
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 inject extra headers into an HTTP response.
The vulnerability exists due to improper neutralization of CRLF sequences in HTTP headers in the Response reason parameter when creating a response with untrusted reason data. A remote attacker can supply a crafted reason value containing carriage return characters to inject extra headers into an HTTP response.
The issue is exploitable only if an application uses untrusted data in the response reason parameter.
How to mitigate CVE-2026-34519
Install security update from vendor's website.