CVE-2026-4923
MEDIUMCVE-2026-4923 is a medium-severity (CVSS 5.9) CWE-1333 vulnerability in path-to-regexp. O3 Security confirms whether CVE-2026-4923 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 wildcards
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:
When using multiple wildcards, combined with at least one parameter, a regular expression can be generated that is vulnerable to ReDoS. This backtracking vulnerability requires the second wildcard to be somewhere other than the end of the path.
Unsafe examples:
/*foo-*bar-:baz /*a-:b-*c-:d /x/*a-:b/*c/y
Safe examples:
/*foo-:bar /*foo-:bar-*baz
Patches:
Upgrade to version 8.4.0.
Workarounds:
If you are using multiple wildcard parameters, you can check the regex output with a tool such as https://makenowjust-labs.github.io/recheck/playground/ to confirm whether a path is vulnerable.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | path-to-regexp | ≥ 8.0.0&&< 8.4.0 | 8.4.0 |
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 8.4.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-4923 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-2026-4923 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-2026-4923. 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-2026-4923 in your dependencies?
O3 detects CVE-2026-4923 across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.