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.
Metrics
Affected Vendors & Products
References
History
Thu, 26 Mar 2026 18:15:00 +0000
| Type | Values Removed | Values Added |
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| Metrics |
ssvc
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Thu, 26 Mar 2026 16:45:00 +0000
| Type | Values Removed | Values Added |
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| 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. | |
| Title | path-to-regexp vulnerable to Regular Expression Denial of Service via multiple route parameters | |
| Weaknesses | CWE-1333 | |
| References |
| |
| Metrics |
cvssV3_1
|
Status: PUBLISHED
Assigner: openjs
Published:
Updated: 2026-03-26T16:52:14.893Z
Reserved: 2026-03-25T20:11:53.714Z
Link: CVE-2026-4867
Updated: 2026-03-26T16:52:11.744Z
Status : Received
Published: 2026-03-26T17:16:42.983
Modified: 2026-03-26T17:16:42.983
Link: CVE-2026-4867
No data.
OpenCVE Enrichment
No data.