Security advisory

{
  "id": "1295d45cce2bc9ca10f94c2d82101d21da9811de57e8380b5c258906919862c3",
  "url": "https://osv.dev/vulnerability/CVE-2021-29492",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "CVE-2021-29492",
    "summary": "Envoy is a cloud-native edge/middle/service proxy. Envoy does not decode escaped slash sequences `%2F` and `%5C` in HTTP URL paths in versions 1.18.2 and before. A remote attacker may craft a path with escaped slashes, e.g. `/something%2F..%2Fadmin`, to bypass access control, e.g. a block on `/admin`. A backend server could then decode slash sequences and normalize path and provide an attacker access beyond the scope provided for by the access control policy. ### Impact Escalation of Privileges when using RBAC or JWT filters with enforcement based on URL path. Users with back end servers that interpret `%2F` and `/` and `%5C` and `\\` interchangeably are impacted. ### Attack Vector URL paths containing escaped slash characters delivered by untrusted client. Patches in versions 1.18.3, 1.17.3, 1.16.4, 1.15.5 contain new path normalization option to decode escaped slash characters. As a workaround, if back end servers treat `%2F` and `/` and `%5C` and `\\` interchangeably and a URL path based access control is configured, one may reconfigure the back end server to not treat `%2F` and `/` and `%5C` and `\\` interchangeably.",
    "evidence": "osv:CVE-2021-29492",
    "products": [],
    "severity": "high",
    "structured": {
      "id": "CVE-2021-29492",
      "aliases": [
        "BIT-envoy-2021-29492",
        "CVE-2021-29492",
        "GHSA-4987-27fx-x6cf"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:L"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/envoyproxy/envoy",
              "type": "GIT",
              "events": [
                {
                  "introduced": "0"
                },
                {
                  "fixed": "623479e875619a71adc2ad0ea3cfc9f67a79e765"
                },
                {
                  "introduced": "8fb3cb86082b17144a80402f5367ae65f06083bd"
                },
                {
                  "fixed": "bf5d0eb44b781ac26ff1513700bcb114b7cf4300"
                },
                {
                  "introduced": "5c801b25cae04f06bf48248c90e87d623d7a6283"
                },
                {
                  "fixed": "46bf743b97d0d3f01ff437b2f10cc0bd9cdfe6e4"
                },
                {
                  "introduced": "345ffe37148b7a35b6e8e04db0300463689e3ff1"
                },
                {
                  "fixed": "98c1c9e9a40804b93b074badad1cdf284b47d58b"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "cpe": "cpe:2.3:a:envoyproxy:envoy:*:*:*:*:*:*:*:*",
                    "range": [
                      {
                        "introduced": "0"
                      },
                      {
                        "fixed": "1.15.5"
                      }
                    ],
                    "source": "CPE_RANGE"
                  },
                  {
                    "cpe": "cpe:2.3:a:envoyproxy:envoy:*:*:*:*:*:*:*:*",
                    "range": [
                      {
                        "introduced": "1.16.0"
                      },
                      {
                        "fixed": "1.16.4"
                      }
                    ],
                    "source": "CPE_RANGE"
                  },
                  {
                    "cpe": "cpe:2.3:a:envoyproxy:envoy:*:*:*:*:*:*:*:*",
                    "range": [
                      {
                        "introduced": "1.17.0"
                      },
                      {
                        "fixed": "1.17.3"
                      }
                    ],
                    "source": "CPE_RANGE"
                  },
                  {
                    "cpe": "cpe:2.3:a:envoyproxy:envoy:*:*:*:*:*:*:*:*",
                    "range": [
                      {
                        "introduced": "1.18.0"
                      },
                      {
                        "fixed": "1.18.3"
                      }
                    ],
                    "source": "CPE_RANGE"
                  }
                ]
              }
            }
          ],
          "versions": [
            "v1.15.4",
            "v1.17.2",
            "v1.18.2",
            "v1.16.3",
            "v1.18.1",
            "v1.18.0",
            "v1.17.1",
            "v1.17.0",
            "v1.15.3",
            "v1.16.2",
            "v1.16.1",
            "v1.16.0",
            "v1.15.2",
            "v1.15.1",
            "v1.15.0",
            "v1.14.0",
            "v1.13.0",
            "v1.12.0",
            "v1.11.0",
            "v1.10.0",
            "v1.9.0",
            "v1.8.0",
            "v1.7.0",
            "v1.6.0",
            "v1.5.0",
            "v1.4.0",
            "v1.3.0",
            "v1.2.0",
            "v1.1.0",
            "v1.0.0"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2021-29492.json"
          }
        }
      ],
      "modified": "2026-10-20T10:54:37.514759614Z",
      "provider": "osv",
      "references": [
        "https://github.com/envoyproxy/envoy/security/advisories/GHSA-4987-27fx-x6cf"
      ],
      "provider_metadata": {}
    },
    "related_cves": [
      {
        "value": "CVE-2021-29492",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 385777,
  "published_at": "2021-05-28T21:15:08.67+00:00"
}