http-proxy-middleware: multipart/form-data field injection via unescaped CRLF in `fixRequestBody`

{
  "id": "492c44cdd8f53c2cf8596d6b0c8201792ab55eaaf39c15782fbd7606ac10e76c",
  "url": "https://osv.dev/vulnerability/CVE-2026-55603",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "http-proxy-middleware: multipart/form-data field injection via unescaped CRLF in `fixRequestBody`",
    "summary": "http-proxy-middleware is node.js http-proxy middleware. From 3.0.4 until 3.0.7 and 4.1.1, fixRequestBody() is the library's documented helper for re-emitting a request body that was already consumed by a body parser. When the outgoing Content-Type is multipart/form-data, it rebuilds the body with handlerFormDataBodyData(), which interpolates each req.body key and value directly into the multipart wire format without neutralizing CR/LF. A \\r\\n inside a value (or key) lets an attacker close the current part and inject an entirely new form part. Because the proxy's own body parser saw a single opaque value, any gateway-side policy or validation performed on req.body is evaluated against a different set of fields than the upstream backend ultimately parses a request/parameter desynchronization across the trust boundary. This vulnerability is fixed in 3.0.7 and 4.1.1.",
    "evidence": "osv:CVE-2026-55603",
    "products": [],
    "severity": "high",
    "structured": {
      "id": "CVE-2026-55603",
      "aliases": [
        "CVE-2026-55603",
        "GHSA-gcq2-9pq2-cxqm"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:H/A:N"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/chimurai/http-proxy-middleware",
              "type": "GIT",
              "events": [
                {
                  "introduced": "01934d33b157b2d49f7099a18ceec165e7502040"
                },
                {
                  "fixed": "8cc4eba839e6cd95ebc073b2b48c4124ed72c302"
                },
                {
                  "introduced": "8f356bcb5fce079460564f729da55814363361a6"
                },
                {
                  "fixed": "b3b98d2846aa6a0cc9a1a08b8b152a634bb4741e"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "cpe": "cpe:2.3:a:chimurai:http-proxy-middleware:*:*:*:*:*:*:*:*",
                    "range": [
                      {
                        "introduced": "3.0.4"
                      },
                      {
                        "fixed": "3.0.7"
                      }
                    ],
                    "source": "CPE_RANGE"
                  },
                  {
                    "cpe": "cpe:2.3:a:chimurai:http-proxy-middleware:*:*:*:*:*:*:*:*",
                    "range": [
                      {
                        "introduced": "4.0.0"
                      },
                      {
                        "fixed": "4.1.1"
                      }
                    ],
                    "source": "CPE_RANGE"
                  }
                ]
              }
            }
          ],
          "versions": [
            "v4.1.0",
            "v3.0.6",
            "v4.1.0-beta.2",
            "v4.1.0-beta.1",
            "v4.1.0-beta.0",
            "v4.0.0",
            "v3.0.5",
            "v3.0.4"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-55603.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:41.570761424Z",
      "provider": "osv",
      "references": [
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/55xxx/CVE-2026-55603.json",
        "https://github.com/chimurai/http-proxy-middleware/security/advisories/GHSA-gcq2-9pq2-cxqm",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-55603"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-93"
        ],
        "cna_assigner": "GitHub_M",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/55xxx/CVE-2026-55603.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-55603",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 509244,
  "published_at": "2026-06-22T20:07:05.034+00:00"
}