critical9.1
CVE-2026-34520
AIOHTTP's C parser (llhttp) accepts null bytes and control characters in response header values - header injection/security bypass
Impact
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.
Affected packages
| Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|
| pip | aiohttp | <= 3.13.3 | 3.13.4 |
Affected products
| Vendor | Product | Affected versions |
|---|---|---|
| Aiohttp | Aiohttp | before 3.13.4 |
Weakness classification
References
- NVD record
- CVE.org record
- GitHub advisory
- https://github.com/aio-libs/aiohttp/commit/9370b9714a7a56003cacd31a9b4ae16eab109ba4
- https://github.com/aio-libs/aiohttp/releases/tag/v3.13.4
- https://github.com/aio-libs/aiohttp/security/advisories/GHSA-63hf-3vf5-4wqf
- https://github.com/advisories/GHSA-63hf-3vf5-4wqf
- https://nvd.nist.gov/vuln/detail/CVE-2026-34520
- https://github.com/pypa/advisory-database/tree/main/vulns/aiohttp/PYSEC-2026-2102.yaml