{"id":"CVE-2026-4867","url":"https://www.cyber-defence.io/tools/cve/CVE-2026-4867","generatedAt":"2026-10-28T02:16:25.078Z","title":"Impact: A bad regular expression is generated any time you have three or more parameters within a single segment, separated by something that is not a period (.).","description":"Impact:\n\nA bad regular expression is generated any time you have three or more parameters within a single segment, separated by something that is not a period (.). For example, /:a-:b-:c or /:a-:b-:c-:d. The backtrack protection added in path-to-regexp@0.1.12 only prevents ambiguity for two parameters. With three or more, the generated lookahead does not block single separator characters, so capture groups overlap and cause catastrophic backtracking.\n\nPatches:\n\nUpgrade to path-to-regexp@0.1.13\n\nCustom regex patterns in route definitions (e.g., /:a-:b([^-/]+)-:c([^-/]+)) are not affected because they override the default capture group.\n\nWorkarounds:\n\nAll versions can be patched by providing a custom regular expression for parameters after the first in a single segment. As long as the custom regular expression does not match the text before the parameter, you will be safe. For example, change /:a-:b-:c to /:a-:b([^-/]+)-:c([^-/]+).\n\nIf paths cannot be rewritten and versions cannot be upgraded, another alternative is to limit the URL length.","published":"2026-03-26T17:16:43.000Z","lastModified":"2026-06-17T10:57:22.000Z","status":"Analyzed","sourceIdentifier":"ce714d77-add3-4f53-aff5-83d477b104bb","cvss":{"version":"3.1","score":7.5,"severity":"HIGH","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"},"cwe":["CWE-1333"],"affected":["pillarjs/path-to-regexp"],"epss":{"score":0.00515,"percentile":0.4362,"date":"2026-10-26","history":[]},"kev":{"listed":false},"exploits":{"count":0,"verified":false,"firstPublished":null,"source":"Exploit-DB (https://gitlab.com/exploit-database/exploitdb)","entries":[]},"verdict":{"level":"high","text":"High impact if exploited, but EPSS currently rates exploitation as unlikely (0.52%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit."},"changes":[],"references":[{"url":"https://blakeembrey.com/posts/2024-09-web-redos","tags":["Technical Description"],"source":"ce714d77-add3-4f53-aff5-83d477b104bb"},{"url":"https://cna.openjsf.org/security-advisories.html","tags":["Third Party Advisory"],"source":"ce714d77-add3-4f53-aff5-83d477b104bb"},{"url":"https://github.com/advisories/GHSA-9wv6-86v2-598j","tags":["Not Applicable"],"source":"ce714d77-add3-4f53-aff5-83d477b104bb"}],"sources":{"nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-4867","epss":"https://www.first.org/epss/","kev":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog","exploitdb":"https://www.exploit-db.com/"},"licence":"CC BY 4.0 — link back to the CVE Explorer if you publish the results; upstream data remains subject to its own terms."}