{"id":"CVE-2026-84380","aliases":["GHSA-pf96-p4fj-6566"],"url":"https://o3.security/vulnerability/CVE-2026-84380","summary":"HTTPX2: Conflicting Content-Length and Transfer-Encoding headers can be auto-generated","details":"HTTPX2 is a next generation HTTP client for Python. Prior to 2.11.0, Request._prepare() in src/httpx2/httpx2/_models.py can add a body-derived Content-Length header to a request that already contains a caller-supplied Transfer-Encoding header because its setdefault() processing checks each default header independently rather than treating the two framing headers as mutually exclusive. Fixed-size byte, JSON, form, and known-length multipart bodies can therefore be serialized over HTTP/1.1 with both headers, allowing request smuggling or connection desynchronization when downstream intermediaries disagree about which framing header takes precedence. This issue is fixed in version 2.11.0.","published":"2026-09-02T17:58:55.520Z","modified":"2026-09-04T03:47:27.315803138Z","cvss":{"score":5.6,"severity":"MEDIUM","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:L"},"epss":{"score":0.00221,"percentile":0.12542,"asOf":"2026-09-08"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"PyPI","name":"httpx2","fixedVersion":"2.11.0"}],"fix":{"url":"https://github.com/pydantic/httpx2/commit/829b93a2393212996f613e635261f777d9ec6eab","label":"pydantic/httpx2@829b93a"},"references":[{"type":"WEB","url":"https://github.com/pydantic/httpx2/releases/tag/v2.11.0"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/84xxx/CVE-2026-84380.json"},{"type":"ADVISORY","url":"https://github.com/pydantic/httpx2/security/advisories/GHSA-pf96-p4fj-6566"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-84380"},{"type":"FIX","url":"https://github.com/pydantic/httpx2/commit/829b93a2393212996f613e635261f777d9ec6eab"},{"type":"FIX","url":"https://github.com/pydantic/httpx2/pull/1137"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-09-04T03:47:27.315803138Z"}}