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GHSA-63hf-3vf5-4wqf

AIOHTTP's C parser (llhttp) accepts null bytes and control characters in response header values - header injection/security bypass

Source: GitHub Advisory Database (reviewed) Low CVE-2026-34520

Packages

EcosystemPackageAffectedFixed in
PyPI aiohttp < 3.13.4 3.13.4

Details

As written in the advisory (Markdown source, shown as plain text).

### Summary The C parser (the default for most installs) accepted null bytes and control characters in request 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. ----- Patch: https://github.com/aio-libs/aiohttp/commit/9370b9714a7a56003cacd31a9b4ae16eab109ba4

References

External links from the advisory. They lead to third-party sites.