CVE-2026-4867
HIGHCVE-2026-4867 is a high-severity (CVSS 7.5) CWE-1333 vulnerability in path-to-regexp. O3 Security confirms whether CVE-2026-4867 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
path-to-regexp vulnerable to Regular Expression Denial of Service via multiple route parameters
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, a proxy for how much of the ecosystem is exposed.
path-to-regexpnpmDescription
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.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | path-to-regexp | all versions | 0.1.13 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for path-to-regexp. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update path-to-regexp to 0.1.13 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-4867 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether CVE-2026-4867 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2026-4867. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-4867 in your dependencies?
O3 detects CVE-2026-4867 across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.