CVE-2026-4867
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.
Affected packages
Versions sourced from the GitHub Security Advisory.
| Package | Affected versions | Patched versions |
|---|---|---|
path-to-regexpnpm | < 0.1.13 | 0.1.13 |
Affected products
1Patches
0No patches discovered yet.
Vulnerability mechanics
AI mechanics synthesis has not run for this CVE yet.
References
7- cna.openjsf.org/security-advisories.htmlnvdThird Party AdvisoryWEB
- github.com/advisories/GHSA-37ch-88jc-xwx2ghsaADVISORY
- github.com/advisories/GHSA-9wv6-86v2-598jnvdNot ApplicableADVISORY
- nvd.nist.gov/vuln/detail/CVE-2026-4867ghsaADVISORY
- blakeembrey.com/posts/2024-09-web-redosnvdTechnical DescriptionWEB
- github.com/pillarjs/path-to-regexp/releases/tag/v.0.1.13ghsaWEB
- github.com/pillarjs/path-to-regexp/security/advisories/GHSA-37ch-88jc-xwx2ghsaWEB
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