Starlette vulnerable to O(n^2) DoS via Range header merging in starlette.responses.FileResponse

{
  "id": "8acb229343fa3a4521a5e518eeab2a36cd51b4c4bcf5f3421bda0ba5a8cfbfa7",
  "url": "https://osv.dev/vulnerability/CVE-2025-62727",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "Starlette vulnerable to O(n^2) DoS via Range header merging in starlette.responses.FileResponse",
    "summary": "Starlette is a lightweight ASGI framework/toolkit. Starting in version 0.39.0 and prior to version 0.49.1 , an unauthenticated attacker can send a crafted HTTP Range header that triggers quadratic-time processing in Starlette's FileResponse Range parsing/merging logic. This enables CPU exhaustion per request, causing denial‑of‑service for endpoints serving files (e.g., StaticFiles or any use of FileResponse). This vulnerability is fixed in 0.49.1.",
    "evidence": "osv:CVE-2025-62727",
    "products": [],
    "severity": "high",
    "structured": {
      "id": "CVE-2025-62727",
      "aliases": [
        "CVE-2025-62727",
        "GHSA-7f5h-v6xp-fcq8",
        "PYSEC-2026-1942"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/kludex/starlette",
              "type": "GIT",
              "events": [
                {
                  "introduced": "65bfd74307f593505aaa4c399f73e4d90cd8aa78"
                },
                {
                  "fixed": "7e4b7428f273dbdc875dcd036d20804bcfc7b2ee"
                },
                {
                  "fixed": "4ea6e22b489ec388d6004cfbca52dd5b147127c5"
                },
                {
                  "fixed": "69ed26a85956ef4bd0161807eb27abf49be7cd3c"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "range": [
                      {
                        "introduced": "0.39.0"
                      },
                      {
                        "fixed": "0.49.1"
                      }
                    ],
                    "source": "AFFECTED_FIELD",
                    "strategy": "StringRangeExpression"
                  },
                  {
                    "range": [
                      {
                        "fixed": "4ea6e22b489ec388d6004cfbca52dd5b147127c5"
                      }
                    ],
                    "source": "REFERENCES_COMMIT"
                  },
                  {
                    "range": [
                      {
                        "fixed": "69ed26a85956ef4bd0161807eb27abf49be7cd3c"
                      }
                    ],
                    "source": "REFERENCES_COMMIT"
                  },
                  {
                    "range": [
                      {
                        "fixed": "7e4b7428f273dbdc875dcd036d20804bcfc7b2ee"
                      }
                    ],
                    "source": "REFERENCES_TAG",
                    "original_tag": "0.49.1"
                  }
                ]
              }
            }
          ],
          "versions": [
            "0.49.0",
            "0.48.0",
            "0.47.3",
            "0.47.2",
            "0.47.1",
            "0.47.0",
            "0.46.2",
            "0.46.1",
            "0.46.0",
            "0.45.3",
            "0.45.2",
            "0.45.1",
            "0.45.0",
            "0.44.0",
            "0.43.0",
            "0.42.0",
            "0.41.3",
            "0.41.2",
            "0.41.1",
            "0.41.0",
            "0.40.0",
            "0.39.2",
            "0.39.1",
            "0.39.0"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2025-62727.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:27.292299622Z",
      "provider": "osv",
      "references": [
        "https://github.com/Kludex/starlette/releases/tag/0.49.1",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/62xxx/CVE-2025-62727.json",
        "https://github.com/Kludex/starlette/security/advisories/GHSA-7f5h-v6xp-fcq8",
        "https://nvd.nist.gov/vuln/detail/CVE-2025-62727",
        "https://github.com/Kludex/starlette/commit/4ea6e22b489ec388d6004cfbca52dd5b147127c5",
        "https://github.com/Kludex/starlette/commit/69ed26a85956ef4bd0161807eb27abf49be7cd3c"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-407"
        ],
        "cna_assigner": "GitHub_M",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/62xxx/CVE-2025-62727.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2025-62727",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 493811,
  "published_at": "2025-10-28T20:14:53.655+00:00"
}