CVE-2021-23384
MEDIUMThe package koa-remove-trailing-slashes before 2.0.2 are vulnerable to Open Redirect via the use of trailing double slashes in the URL when accessing the vulnerable endpoint (such as…
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Description
The package koa-remove-trailing-slashes before 2.0.2 are vulnerable to Open Redirect via the use of trailing double slashes in the URL when accessing the vulnerable endpoint (such as https://example.com//attacker.example/). The vulnerable code is in index.js::removeTrailingSlashes(), as the web server uses relative URLs instead of absolute URLs.
Affected Products
koa-remove-trailing-slasheskoa-remove-trailing-slashes_projectResearch 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
Vendor / applianceDetect
Inventory every koa-remove-trailing-slashes_project koa-remove-trailing-slashes deployment and check each version against the affected-products list above. Because the exploit targets the running system rather than your application code, also watch for exploitation at the network and runtime layer — O3 flags the exploit behaviour from runtime telemetry and egress traffic even before a vulnerable build is confirmed.
Fix
Apply the koa-remove-trailing-slashes_project koa-remove-trailing-slashes security patch or hotfix for CVE-2021-23384 on the affected version, following the vendor advisory for your exact build.
Workarounds
Cut exposure now: restrict the management/admin interface to trusted networks, segment the device, and apply the vendor's recommended configuration mitigations and any WAF/IPS signature. O3's runtime protection blocks the exploit chain at execution, holding the line on unpatched or end-of-life systems until you can patch.
How O3 protects you
O3 detects and blocks CVE-2021-23384 exploitation at runtime: eBPF exploit-chain detection, plus L7 egress monitoring that catches the post-exploitation callback and severs the attacker's outbound channel.
Tailored to CVE-2021-23384. 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-2021-23384 being exploited in your environment?
O3's eBPF runtime sensors and L7 egress monitoring detect and block the CVE-2021-23384 exploit chain at execution — protecting unpatched and end-of-life systems until the vendor patch is applied.