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.
Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).
| Vendor | Product | Default status | Versions | ||||||
|---|---|---|---|---|---|---|---|---|---|
| path-to-regexp | path-to-regexp | unaffected |
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Solution
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Workaround
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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
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Projects
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MITRE
Status: PUBLISHED
Assigner: openjs
Published:
Updated: 2026-03-26T16:52:14.893Z
Reserved: 2026-03-25T20:11:53.714Z
Link: CVE-2026-4867
Vulnrichment
Updated: 2026-03-26T16:52:11.744Z
NVD
Status : Received
Published: 2026-03-26T17:16:42.983
Modified: 2026-03-26T17:16:42.983
Link: CVE-2026-4867
Redhat
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OpenCVE Enrichment
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