{"id":"CVE-2026-34520","aliases":["GHSA-63hf-3vf5-4wqf","PYSEC-2026-2102"],"url":"https://o3.security/vulnerability/CVE-2026-34520","summary":"AIOHTTP: C parser (llhttp) accepts null bytes and control characters in response header values - header injection / security bypass","details":"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.","published":"2026-04-01T20:27:48.350Z","modified":"2026-08-12T03:51:22.036485111Z","cvss":null,"epss":null,"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"PyPI","name":"aiohttp","fixedVersion":"3.13.4"}],"fix":{"url":"https://github.com/aio-libs/aiohttp/commit/9370b9714a7a56003cacd31a9b4ae16eab109ba4","label":"aio-libs/aiohttp@9370b97"},"references":[{"type":"WEB","url":"https://github.com/aio-libs/aiohttp/releases/tag/v3.13.4"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/34xxx/CVE-2026-34520.json"},{"type":"ADVISORY","url":"https://github.com/aio-libs/aiohttp/security/advisories/GHSA-63hf-3vf5-4wqf"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-34520"},{"type":"FIX","url":"https://github.com/aio-libs/aiohttp/commit/9370b9714a7a56003cacd31a9b4ae16eab109ba4"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-12T03:51:22.036485111Z"}}