CVE-2026-4867
path-to-regexp vulnerable to Regular Expression Denial of Service via multiple route parameters
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 [email protected] 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 [email protected] 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.
How to fix CVE-2026-4867
To remediate CVE-2026-4867, upgrade the affected package to a fixed version below.
- —upgrade to 1.0.1-1 or later
- —upgrade to 0.1.13 or later
Is CVE-2026-4867 being exploited?
Low — EPSS is 0.0%, meaning exploitation activity has not been observed at scale.
Affected packages (2)
- from 0, < 1.0.1-1
- from 0, < 0.1.13
CVSS scores
| Source | Version | Severity | Vector |
|---|---|---|---|
| osv | CVSS 3.1 | HIGH7.5 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H |