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CVE-2026-34520— AIOHTTP: C parser (llhttp) accepts null bytes and control characters in response header values - header injection / security bypass

Quick assessment

Affected
aio-libs aiohttp
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

aiohttp是aio-libs开源的一个开源的用于 asyncio 和 Python 的异步 HTTP 客户端/服务器框架。 AIOHTTP 3.13.4之前版本存在注入漏洞，该漏洞源于C解析器接受响应标头中的空字节和控制字符。

AI Predicted 5.3 Difficulty: Moderate EPSS 0.68% · P51

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application
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I. Basic Information for CVE-2026-34520

Vulnerability Information
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Vulnerability Title
AIOHTTP: C parser (llhttp) accepts null bytes and control characters in response header values - header injection / security bypass
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
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/E:U
Source: CVE Program / CVE List V5
Vulnerability Type
HTTP头部中CRLF序列转义处理不恰当(HTTP响应分割)
Source: CVE Program / CVE List V5
Vulnerability Title
aiohttp 注入漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
aiohttp是aio-libs开源的一个开源的用于 asyncio 和 Python 的异步 HTTP 客户端/服务器框架。 AIOHTTP 3.13.4之前版本存在注入漏洞，该漏洞源于C解析器接受响应标头中的空字节和控制字符。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
aio-libs aiohttp < 3.13.4 -

II. Public POCs for CVE-2026-34520

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III. Intelligence Information for CVE-2026-34520

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Patches & Fixes for CVE-2026-34520 (1)

Vendor Advisories for CVE-2026-34520 (1)

Same Patch Batch · aio-libs · 2026-04-01 · 10 CVEs total

CVE-2026-22815 AIOHTTP: Uncapped memory usage possible through aiohttp allowing unlimited trailer headers
CVE-2026-34513 AIOHTTP: Denial of Service (DoS) via Unbounded DNS Cache in TCPConnector
CVE-2026-34516 AIOHTTP: Multipart Header Size Bypass
CVE-2026-34514 AIOHTTP: CRLF injection in multipart part content type header construction
CVE-2026-34525 AIOHTTP: Duplicate Host header accepted
CVE-2026-34517 AIOHTTP: Late size enforcement for non-file multipart fields causes memory DoS
CVE-2026-34519 AIOHTTP: HTTP response splitting via \r in reason phrase
CVE-2026-34518 AIOHTTP: Cookie and Proxy-Authorization headers leaked on cross-origin redirect
CVE-2026-34515 AIOHTTP: UNC SSRF/NTLMv2 Credential Theft/Local File Read in static resource handler on Wi

IV. Related Vulnerabilities

Same product: aiohttp
Same vendor: aio-libs
Same weakness: CWE-113

V. Comments for CVE-2026-34520

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