{"id":"CVE-2025-57804","aliases":["GHSA-847f-9342-265h","PYSEC-2026-1435"],"url":"https://o3.security/vulnerability/CVE-2025-57804","summary":"h2 allows HTTP Request Smuggling due to illegal characters in headers","details":"h2 is a pure-Python implementation of a HTTP/2 protocol stack. Prior to version 4.3.0, an HTTP/2 request splitting vulnerability allows attackers to perform request smuggling attacks by injecting CRLF characters into headers. This occurs when servers downgrade HTTP/2 requests to HTTP/1.1 without properly validating header names/values, enabling attackers to manipulate request boundaries and bypass security controls. This issue has been patched in version 4.3.0.","published":"2025-08-25T21:04:52.642Z","modified":"2026-08-12T03:51:27.298010583Z","cvss":null,"epss":{"score":0.01711,"percentile":0.75586,"asOf":"2026-08-24"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"PyPI","name":"h2","fixedVersion":"4.3.0"}],"fix":{"url":"https://github.com/python-hyper/h2/commit/035e9899f95e3709af098f578bfc3cd302298e3a","label":"python-hyper/h2@035e989"},"references":[{"type":"WEB","url":"https://lists.debian.org/debian-lts-announce/2025/09/msg00004.html"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/57xxx/CVE-2025-57804.json"},{"type":"ADVISORY","url":"https://github.com/python-hyper/h2/security/advisories/GHSA-847f-9342-265h"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2025-57804"},{"type":"FIX","url":"https://github.com/python-hyper/h2/commit/035e9899f95e3709af098f578bfc3cd302298e3a"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-12T03:51:27.298010583Z"}}