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MEDIUM severity

CVE-2021-23384 — koa-remove-trailing-slash…

MEDIUMFix: vgno/koa-remove-trailing-slashes@e7ce400

CVE-2021-23384 is a medium-severity (CVSS 5.4) Open Redirect vulnerability in koa-remove-trailing-slashes. 1 public exploit reference exists, so weaponization risk is real. A fix is available for koa-remove-trailing-slashes — see the affected versions and patch details below.

Open Redirect in koa-remove-trailing-slashes

Published
Updated
Affected
1 pkg
Patched
1 / 1
Exploits
1 known
Exploitation data as of Oct 10, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗
0.8%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs56th percentile — riskier than 56% of all scored CVEsHighest risk
0.00%0.45%0.89%1.33%0.2%0.8%Apr 26Aug 26Oct 26

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2021-23384 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 385,386 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

1 pkg affected
📦koa-remove-trailing-slashes

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects npm packages — download data is not available via public APIs for these ecosystems.

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 Packages

1 total 1 fixed
EcosystemPackageVulnerable rangeFix
📦npmkoa-remove-trailing-slashesall versions2.0.2npm install koa-remove-trailing-slashes@2.0.2

Affected Products

1 product · 1 configurations
Application
koa-remove-trailing-slasheskoa-remove-trailing-slashes_project
< 2.0.2
range
Exploits & PoCs
1

Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.

The package koa-remove-trailing-slashes before 2.0.2 are vulnerable to O…

snyk.ioNVDMay 2021

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for koa-remove-trailing-slashes, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update koa-remove-trailing-slashes to 2.0.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-23384 is resolved across your whole dependency graph.

  3. Workarounds

    Stop reflecting attacker-controlled destinations: resolve every redirect target against an allowlist of paths or hosts you own, prefer a server-side key over a full URL in the request, and reject absolute URLs entirely where the flow only ever needs a relative one.

Frequently Asked Questions

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.
O3 Security · Impact-Aware SCA

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