{"id":"CVE-2026-34525","aliases":["GHSA-c427-h43c-vf67","PYSEC-2026-2103"],"url":"https://o3.security/vulnerability/CVE-2026-34525","summary":"AIOHTTP: Duplicate Host header accepted","details":"### Summary\n\nMultiple Host headers were allowed in aiohttp.\n\n### Impact\n\nMostly this doesn't affect aiohttp security itself, but if a reverse proxy is applying security rules depending on the target Host, it is theoretically possible that the proxy and aiohttp could process different host names, possibly resulting in bypassing a security check on the proxy and getting a request processed by aiohttp in a privileged sub app when using `Application.add_domain()`.\n\n-----\n\nPatch: https://github.com/aio-libs/aiohttp/commit/e00ca3cca92c465c7913c4beb763a72da9ed8349\nPatch: https://github.com/aio-libs/aiohttp/commit/53e2e6fc58b89c6185be7820bd2c9f40216b3000","published":"2026-04-01T20:28:46.652Z","modified":"2026-08-12T03:51:23.220992211Z","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/53e2e6fc58b89c6185be7820bd2c9f40216b3000","label":"aio-libs/aiohttp@53e2e6f"},"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-2026-34525.json"},{"type":"ADVISORY","url":"https://github.com/aio-libs/aiohttp/security/advisories/GHSA-c427-h43c-vf67"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-34525"},{"type":"FIX","url":"https://github.com/aio-libs/aiohttp/commit/53e2e6fc58b89c6185be7820bd2c9f40216b3000"},{"type":"FIX","url":"https://github.com/aio-libs/aiohttp/commit/e00ca3cca92c465c7913c4beb763a72da9ed8349"},{"type":"PACKAGE","url":"https://github.com/aio-libs/aiohttp"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-12T03:51:23.220992211Z"}}