CVE-2026-4867 (High) detected in path-to-regexp-0.1.12.tgz

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CVE-2026-4867 - High Severity Vulnerability

Vulnerable Library - path-to-regexp-0.1.12.tgz

Express style path to RegExp utility

Library home page: https://registry.npmjs.org/path-to-regexp/-/path-to-regexp-0.1.12.tgz

Path to dependency file: /package.json

Path to vulnerable library: /package.json

Dependency Hierarchy:

• express-4.21.2.tgz (Root Library)
  • ❌ path-to-regexp-0.1.12.tgz (Vulnerable Library)

Found in base branch: csl

Vulnerability Details

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 (.). 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.
Patches:
Upgrade to path-to-regexp@0.1.13
Custom regex patterns in route definitions (e.g., /:a-:b([^-/]+)-:c([^-/]+)) are not affected because they override the default capture group.
Workarounds:
All 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([^-/]+).
If paths cannot be rewritten and versions cannot be upgraded, another alternative is to limit the URL length.

Publish Date: 2026-03-26

URL: CVE-2026-4867

CVSS 3 Score Details (7.5)

Base Score Metrics:

• Exploitability Metrics:
  • Attack Vector: Network
  • Attack Complexity: Low
  • Privileges Required: None
  • User Interaction: None
  • Scope: Unchanged
• Impact Metrics:
  • Confidentiality Impact: None
  • Integrity Impact: None
  • Availability Impact: High

For more information on CVSS3 Scores, click here.

Suggested Fix

Type: Upgrade version

Origin: GHSA-37ch-88jc-xwx2

Release Date: 2026-03-26

Fix Resolution: path-to-regexp - 0.1.13