CVE-2026-34520: CWE-113: Improper Neutralization of CRLF Sequences in HTTP Headers ('HTTP Request/Response Splitting') in aio-libs aiohttp
AIOHTTP versions prior to 3.13.4 contain a vulnerability where the C parser accepts null bytes and control characters in HTTP response headers, leading to improper neutralization of CRLF sequences (HTTP request/response splitting). This issue has been fixed in version 3.13.4. The vulnerability has a low severity score of 2.7 and does not require user interaction or privileges to exploit.
AI Analysis
Technical Summary
CVE-2026-34520 describes a vulnerability in aio-libs aiohttp, an asynchronous HTTP client/server framework for Python. Before version 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 addressed and patched in aiohttp version 3.13.4.
Potential Impact
The vulnerability allows an attacker to inject CRLF sequences into HTTP response headers by exploiting the acceptance of null bytes and control characters. This can lead to HTTP request/response splitting attacks, which may affect the integrity of HTTP communications. However, the CVSS score of 2.7 indicates a low severity impact, with no required privileges or user interaction for exploitation and no known exploits in the wild.
Mitigation Recommendations
Upgrade aiohttp to version 3.13.4 or later, where the vulnerability has been patched. No other mitigations are necessary as the issue is resolved in the official fix.
CVE-2026-34520: CWE-113: Improper Neutralization of CRLF Sequences in HTTP Headers ('HTTP Request/Response Splitting') in aio-libs aiohttp
Description
AIOHTTP versions prior to 3.13.4 contain a vulnerability where the C parser accepts null bytes and control characters in HTTP response headers, leading to improper neutralization of CRLF sequences (HTTP request/response splitting). This issue has been fixed in version 3.13.4. The vulnerability has a low severity score of 2.7 and does not require user interaction or privileges to exploit.
CVSS v4.0
Score 2.7low
Affected software
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Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
CVE-2026-34520 describes a vulnerability in aio-libs aiohttp, an asynchronous HTTP client/server framework for Python. Before version 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 addressed and patched in aiohttp version 3.13.4.
Potential Impact
The vulnerability allows an attacker to inject CRLF sequences into HTTP response headers by exploiting the acceptance of null bytes and control characters. This can lead to HTTP request/response splitting attacks, which may affect the integrity of HTTP communications. However, the CVSS score of 2.7 indicates a low severity impact, with no required privileges or user interaction for exploitation and no known exploits in the wild.
Mitigation Recommendations
Upgrade aiohttp to version 3.13.4 or later, where the vulnerability has been patched. No other mitigations are necessary as the issue is resolved in the official fix.
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: 04/01/2026, 20:53:18 UTC
Last enriched: 07/16/2026, 10:58:23 UTC
Last updated: 07/31/2026, 19:22:58 UTC
Views: 139
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