Clerk: SSRF in the opt-in clerkFrontendApiProxy feature may leak secret keys to unintended host
Summary
The clerkFrontendApiProxy function in @clerk/backend is vulnerable to Server-Side Request Forgery (SSRF). An unauthenticated attacker can craft a request path that causes the proxy to send the application's Clerk-Secret-Key to an attacker-controlled server.
Affected packages
Only applications that have opted into the frontendApiProxy feature are affected. This feature is not enabled by default. Users of @clerk/nextjs are not affected due to how the framework handles repeated / in request paths.
| Package | Affected versions | Fixed version |
|---|---|---|
@clerk/backend |
>= 3.0.0, <= 3.2.2 |
3.2.3 |
@clerk/express |
>= 2.0.0, <= 2.0.6 |
2.0.7 |
@clerk/hono |
>= 0.1.0, <= 0.1.4 |
0.1.5 |
@clerk/fastify |
>= 3.1.0, <= 3.1.4 |
3.1.5 |
Search your codebase for the frontendApiProxy option. If none of the patterns below appear in your code, you are not affected.
@clerk/express
app.use(clerkMiddleware({ frontendApiProxy: { enabled: true } }));@clerk/hono
app.use('*', clerkMiddleware({ frontendApiProxy: { enabled: true } }));@clerk/fastify
fastify.register(clerkPlugin, { frontendApiProxy: { enabled: true } });@clerk/backend
import { clerkFrontendApiProxy } from '@clerk/backend/proxy';A quick way to check across your entire project:
grep -r "frontendApiProxy\|clerkFrontendApiProxy" .If there are no matches, you are not using this feature.
Recommended actions
Clerk's internal logs show no evidence of users utilizing the built-in proxy with the impacted versions. Despite that, if you are on an impacted version and use the built-in proxy we recommend upgrading and rotating your Clerk Secret Key immediately.
- Upgrade to the patched version of
@clerk/backend(and@clerk/express,@clerk/hono, etc.) - Rotate your Clerk Secret Key after upgrading - if an attacker exploited this vulnerability, they may have captured your key. Rotate it in the Clerk Dashboard under API Keys. You should deploy your application with the updated key before revoking the existing key.
- Audit access logs for requests to your proxy endpoint (
/__clerk/by default) containing double slashes in the path.
Credit
Discovered during an internal code audit.
Affected software
Click a technology to see all vulnerabilities affecting it.
| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| npm package | @clerk/backend | >= 3.0.0, < 3.2.3 | 3.2.3 |
| npm package | @clerk/express | >= 2.0.0, < 2.0.7 | 2.0.7 |
| npm package | @clerk/fastify | >= 3.1.0, < 3.1.5 | 3.1.5 |
| npm package | @clerk/hono | >= 0.1.0, < 0.1.5 | 0.1.5 |
References
- CVSS vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N- Weakness (CWE)
CWE-918- Platform
- npm
- Package
@clerk/backend, @clerk/express, @clerk/fastify- Disclosed
- 27.03.2026
- Updated
- 11.10.2026 10:22
Sources and licenses
OSV / GitHub Advisory Database - GHSA-gjxx-92w9-8v8f - CC BY 4.0
Vulnerability history: @clerk/express
All published vulnerabilities of this package (npm package), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 3
- First → latest
- 07.2025 04.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- High 3
Disclosures per year
- 2025: 1
- 2026: 2
-
Clerk: SSRF in the opt-in clerkFrontendApiProxy feature may leak secret keys to unintended host this entry
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