Protego: Exponential backtracking ReDoS in robots.txt URL wildcard matching

{
  "id": "f932bf76be9fc4018fbc3b13301c841eb6ae058b0cd608b2b826682e9936ed29",
  "url": "https://osv.dev/vulnerability/CVE-2026-55520",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "Protego: Exponential backtracking ReDoS in robots.txt URL wildcard matching",
    "summary": "Protego is a pure-Python robots.txt parser with support for modern conventions. Prior to 0.6.2, protego._urlpattern._URLPattern._prepare_pattern_for_regex translates every asterisk in an Allow or Disallow directive into a lazy regular-expression wildcard, so a directive containing many asterisks creates exponential backtracking. After protego.Protego.parse processes a crafted robots.txt file, protego.Protego.can_fetch can spend an attacker-controlled period matching a near-miss URL and deny service to the crawler. The vulnerable path is src/protego/_urlpattern.py in the _URLPattern match logic. This issue is fixed in version 0.6.2.",
    "evidence": "osv:CVE-2026-55520",
    "products": [],
    "severity": "high",
    "structured": {
      "id": "CVE-2026-55520",
      "aliases": [
        "CVE-2026-55520",
        "GHSA-wjmf-p669-5m5p",
        "PYSEC-2026-3906"
      ],
      "metrics": [
        {
          "type": "CVSS_V4",
          "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/scrapy/protego",
              "type": "GIT",
              "events": [
                {
                  "introduced": "0"
                },
                {
                  "fixed": "efe5039d39ee51f117acd0b01ffd8109ae265c22"
                },
                {
                  "fixed": "785940181659bf440ba82f1da148fade5087e858"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "range": [
                      {
                        "introduced": "0"
                      },
                      {
                        "fixed": "0.6.2"
                      }
                    ],
                    "source": "AFFECTED_FIELD",
                    "strategy": "StringRangeExpression"
                  },
                  {
                    "range": [
                      {
                        "fixed": "785940181659bf440ba82f1da148fade5087e858"
                      }
                    ],
                    "source": "REFERENCES_COMMIT"
                  },
                  {
                    "range": [
                      {
                        "fixed": "efe5039d39ee51f117acd0b01ffd8109ae265c22"
                      }
                    ],
                    "source": "REFERENCES_TAG",
                    "original_tag": "0.6.2"
                  }
                ]
              }
            }
          ],
          "versions": [
            "0.6.1",
            "0.6.0",
            "0.5.0",
            "0.4.0",
            "0.3.1",
            "0.3.0",
            "0.2.1",
            "0.2.0",
            "0.1.16",
            "0.1.15",
            "0.1.14",
            "0.1.13",
            "0.1.12",
            "0.1.11",
            "0.1.10",
            "0.1.9",
            "0.1.8",
            "0.1.7",
            "0.1.6",
            "v0.1.2",
            "0.1.5",
            "0.1.4",
            "0.1.3",
            "v0.1.1",
            "v0.1"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-55520.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:28.009072736Z",
      "provider": "osv",
      "references": [
        "https://github.com/scrapy/protego/releases/tag/0.6.2",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/55xxx/CVE-2026-55520.json",
        "https://github.com/scrapy/protego/security/advisories/GHSA-wjmf-p669-5m5p",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-55520",
        "https://github.com/scrapy/protego/commit/785940181659bf440ba82f1da148fade5087e858"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-1333",
          "CWE-400"
        ],
        "cna_assigner": "GitHub_M",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/55xxx/CVE-2026-55520.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-55520",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 494800,
  "published_at": "2026-08-28T18:42:38.334+00:00"
}