GHSA-63hf-3vf5-4wqf: AIOHTTP's C parser (llhttp) accepts null bytes and control characters in response header values - header injection/security bypass
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
Details
Original advisory: https://github.com/advisories/GHSA-63hf-3vf5-4wqf
Exploitation outlook
EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.
- Low exploitation riskCVE-2026-345200.46% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 38% of all scored CVEs.
Referenced CVEs
| CVE | CSIRTS overview | External |
|---|---|---|
| CVE-2026-34520 | coverage & exploitation status | NVD · CVE.org |
Same CVEs, other sources
How other CERTs, PSIRTs and databases cover the vulnerabilities in this advisory.
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