CRITICAL 9.1
GHSA-63hf-3vf5-4wqf
AIOHTTP's C parser (llhttp) accepts null bytes and control characters in response header values - header injection/security bypass
Details
### Summary
The C parser (the default for most installs) accepted null bytes and control characters is response headers.
### Impact
An attacker could send header values that are interpreted differently than expected due to the presence of control characters. For example, `request.url.origin()` may return a different value than the raw Host header, or what a reverse proxy interpreted it as., potentially resulting in some kind of security bypass.
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Patch: https://github.com/aio-libs/aiohttp/commit/9370b9714a7a56003cacd31a9b4ae16eab109ba4
Are you affected?
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Affected packages
References
- https://github.com/aio-libs/aiohttp/security/advisories/GHSA-63hf-3vf5-4wqf [WEB]
- https://nvd.nist.gov/vuln/detail/CVE-2026-34520 [ADVISORY]
- https://github.com/aio-libs/aiohttp/commit/9370b9714a7a56003cacd31a9b4ae16eab109ba4 [WEB]
- https://github.com/aio-libs/aiohttp [PACKAGE]
- https://github.com/aio-libs/aiohttp/releases/tag/v3.13.4 [WEB]