CVE-2026-34520: CWE-113: Improper Neutralization of CRLF Sequences in HTTP Headers ('HTTP Request/Response Splitting') in aio-libs aiohttp
AIOHTTP is an asynchronous HTTP client/server framework for asyncio and Python. Prior to version 3.13.4, the C parser (the default for most installs) accepted null bytes and control characters in response headers. This issue has been patched in version 3.13.4.
AI Analysis
Technical Summary
The vulnerability CVE-2026-34520 affects aiohttp versions before 3.13.4. The default C parser allowed null bytes and control characters in HTTP response headers, which constitutes improper neutralization of CRLF sequences (CWE-113). This flaw could potentially enable HTTP request/response splitting attacks. The issue was fixed in version 3.13.4 of aiohttp.
Potential Impact
The vulnerability has a CVSS 4.0 base score of 2.7, indicating low severity. It allows injection of control characters into HTTP response headers, which could lead to HTTP request/response splitting. However, there are no known exploits in the wild, and the impact is limited by the low severity rating.
Mitigation Recommendations
A fix is available in aiohttp version 3.13.4. Users should upgrade to version 3.13.4 or later to remediate this vulnerability. No other mitigation steps are indicated.
CVE-2026-34520: CWE-113: Improper Neutralization of CRLF Sequences in HTTP Headers ('HTTP Request/Response Splitting') in aio-libs aiohttp
Description
AIOHTTP is an asynchronous HTTP client/server framework for asyncio and Python. Prior to version 3.13.4, the C parser (the default for most installs) accepted null bytes and control characters in response headers. This issue has been patched in version 3.13.4.
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
The vulnerability CVE-2026-34520 affects aiohttp versions before 3.13.4. The default C parser allowed null bytes and control characters in HTTP response headers, which constitutes improper neutralization of CRLF sequences (CWE-113). This flaw could potentially enable HTTP request/response splitting attacks. The issue was fixed in version 3.13.4 of aiohttp.
Potential Impact
The vulnerability has a CVSS 4.0 base score of 2.7, indicating low severity. It allows injection of control characters into HTTP response headers, which could lead to HTTP request/response splitting. However, there are no known exploits in the wild, and the impact is limited by the low severity rating.
Mitigation Recommendations
A fix is available in aiohttp version 3.13.4. Users should upgrade to version 3.13.4 or later to remediate this vulnerability. No other mitigation steps are indicated.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- GitHub_M
- Date Reserved
- 2026-03-30T16:03:31.047Z
- Cvss Version
- 4.0
- State
- PUBLISHED
Threat ID: 69cd85bee6bfc5ba1df9d440
Added to database: 4/1/2026, 8:53:18 PM
Last enriched: 4/9/2026, 10:39:38 PM
Last updated: 5/15/2026, 8:06:43 AM
Views: 67
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