{"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":"### Summary\n\nThe C parser (the default for most installs) accepted null bytes and control characters in request headers.\n\n### Impact\n\nAn 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.\n\n-----\n\nPatch: https://github.com/aio-libs/aiohttp/commit/9370b9714a7a56003cacd31a9b4ae16eab109ba4","published":"2026-04-01T20:27:48.350Z","modified":"2026-10-28T02:30:50.736667814Z","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"},{"type":"PACKAGE","url":"https://github.com/aio-libs/aiohttp"},{"type":"WEB","url":"https://github.com/pypa/advisory-database/tree/main/vulns/aiohttp/PYSEC-2026-2102.yaml"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-10-28T02:30:50.736667814Z"}}