CVE-2026-34520 — HTTP Request/Response Splitting in Aiohttp

CWE-113 — HTTP Request/Response SplittingCWE-1286 — Improper Validation of Syntactic Correctness of Input8 documents7 sources
Severity
2.7LOWNVD
EPSS
0.1%
top 82.67%
CISA KEV
Not in KEV
Exploit
No known exploits
Affected products
2
Aio-libs AiohttpAiohttp
Timeline
PublishedApr 1

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.

CVSS vector

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

Affected Packages2 packages

▶PyPIaiohttp/aiohttp< 3.13.4
▶CVEListV5aio-libs/aiohttp< 3.13.4

🔴Vulnerability Details

4
OSV
CVE-2026-34520: AIOHTTP is an asynchronous HTTP client/server framework for asyncio and Python↗2026-04-01
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OSV
AIOHTTP's C parser (llhttp) accepts null bytes and control characters in response header values - header injection/security bypass↗2026-04-01
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GHSA
AIOHTTP's C parser (llhttp) accepts null bytes and control characters in response header values - header injection/security bypass↗2026-04-01
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CVEList
AIOHTTP: C parser (llhttp) accepts null bytes and control characters in response header values - header injection / security bypass↗2026-04-01
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📋Vendor Advisories

2
Red Hat
aiohttp: AIOHTTP: Header injection vulnerability due to improper character handling↗2026-04-01
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Debian
CVE-2026-34520: python-aiohttp - AIOHTTP is an asynchronous HTTP client/server framework for asyncio and Python. ...↗2026
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🕵️Threat Intelligence

1
Wiz
CVE-2026-34520 Impact, Exploitability, and Mitigation Steps | Wiz↗
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CVE-2026-34520 — HTTP Request/Response Splitting | cvebase