CVE-2021-3189
MEDIUMCVE-2021-3189 is a medium-severity (CVSS 6.1) Open Redirect vulnerability in slashify. 1 public exploit reference exists, so weaponization risk is real. O3 Security confirms whether CVE-2021-3189 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Open redirect in Slashify
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.
slashifynpmDescription
The package is an Express middleware that normalises routes by stripping any final slash, redirecting, for example, bookings/latest/ to bookings/latest. However, it does not validate the path it redirects to in any way. In particular, if the path starts with two slashes (or two backslashes, or a slash and a backslash, etc.) it may redirect to a different domain.
Consider the example from the docs. Assume we have run it and started a server on localhost:3000, then visiting localhost:3000///github.com/ redirects you to https://github.com.
Recommendation
This vulnerability is currently un-patched in the slashify package so there is no known safe version of this package. Discontinuing use of slashify is recommended.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | slashify | all versions | No fix |
Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for slashify. 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.
Remediation status
No patched version of slashify has shipped for CVE-2021-3189 yet. Where your build allows, override or pin the dependency away from the vulnerable range, and apply any maintainer-recommended mitigation.
Mitigate without a patch
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-2021-3189 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-2021-3189. 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-2021-3189 in your dependencies?
O3 detects CVE-2021-3189 across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.