HTTPX2: Conflicting Content-Length and Transfer-Encoding headers can be auto-generated

{
  "id": "ecbb38b084a48aecf235e658b64133a98a4236d2c1d5aebaaf8e864d181b82bf",
  "url": "https://osv.dev/vulnerability/CVE-2026-84380",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "HTTPX2: Conflicting Content-Length and Transfer-Encoding headers can be auto-generated",
    "summary": "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.",
    "evidence": "osv:CVE-2026-84380",
    "products": [],
    "severity": "medium",
    "structured": {
      "id": "CVE-2026-84380",
      "aliases": [
        "CVE-2026-84380",
        "GHSA-pf96-p4fj-6566",
        "PYSEC-2026-3849"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:L"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/pydantic/httpx2",
              "type": "GIT",
              "events": [
                {
                  "introduced": "0"
                },
                {
                  "fixed": "2b13fa92e4181d5e0f56772205360b2aa12f109d"
                },
                {
                  "fixed": "829b93a2393212996f613e635261f777d9ec6eab"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "range": [
                      {
                        "introduced": "0"
                      },
                      {
                        "fixed": "2.11.0"
                      }
                    ],
                    "source": "AFFECTED_FIELD",
                    "strategy": "StringRangeExpression"
                  },
                  {
                    "range": [
                      {
                        "fixed": "829b93a2393212996f613e635261f777d9ec6eab"
                      }
                    ],
                    "source": "REFERENCES_COMMIT"
                  },
                  {
                    "range": [
                      {
                        "fixed": "2b13fa92e4181d5e0f56772205360b2aa12f109d"
                      }
                    ],
                    "source": "REFERENCES_TAG",
                    "original_tag": "v2.11.0"
                  }
                ]
              }
            }
          ],
          "versions": [
            "v2.10.0",
            "v2.9.1",
            "v2.9.0",
            "v2.8.0",
            "v2.7.0",
            "v2.6.0",
            "v2.5.0",
            "v2.4.0",
            "v2.3.0",
            "v2.2.0",
            "v2.1.0",
            "v2.0.0",
            "v2.0.0b1"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-84380.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:42.456507325Z",
      "provider": "osv",
      "references": [
        "https://github.com/pydantic/httpx2/releases/tag/v2.11.0",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/84xxx/CVE-2026-84380.json",
        "https://github.com/pydantic/httpx2/security/advisories/GHSA-pf96-p4fj-6566",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-84380",
        "https://github.com/pydantic/httpx2/commit/829b93a2393212996f613e635261f777d9ec6eab",
        "https://github.com/pydantic/httpx2/pull/1137"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-444"
        ],
        "cna_assigner": "GitHub_M",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/84xxx/CVE-2026-84380.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-84380",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 510019,
  "published_at": "2026-09-02T17:58:55.52+00:00"
}