CVE-2026-4867: path-to-regexp

Vulnerability summary

CVE-2026-4867 is a high (CVSS 7.5) vulnerability in path-to-regexp. EPSS estimates a 0.62% chance of exploitation in the next 30 days, higher than 48.5% of scored vulnerabilities.

Timeline

1. 26-03-2026
   PublishedVulnerability first disclosed.
2. 26-03-2026
   Last modifiedVulnerability information updated.

Description

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.

• CWE-1333Inefficient Regular Expression ComplexityThe product uses a regular expression with a worst-case computational complexity that is inefficient and possibly exponential.