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.
Impact
Untrusted input controls the target URL of a server-initiated request, which may reach internal services not otherwise accessible from outside. Typical impact: access to internal metadata services, internal APIs, or cloud credentials.
CVE-2026-34076 has a CVSS score of 7.4 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (3.2.3, 2.0.7, 0.1.5, 3.1.5); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
Remediation advice
@clerk/backend to 3.2.3 or later; @clerk/express to 2.0.7 or later; @clerk/hono to 0.1.5 or later; @clerk/fastify to 3.1.5 or later
Kodem Kai can prioritize this vulnerability in your dependency tree and generate a fix recommendation.
Frequently Asked Questions
- What is CVE-2026-34076? CVE-2026-34076 is a high-severity server-side request forgery (SSRF) vulnerability in @clerk/backend (npm), affecting versions >= 3.0.0, <= 3.2.2. It is fixed in 3.2.3, 2.0.7, 0.1.5, 3.1.5. Untrusted input controls the target URL of a server-initiated request, which may reach internal services not otherwise accessible from outside.
- How severe is CVE-2026-34076? CVE-2026-34076 has a CVSS score of 7.4 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which packages are affected by CVE-2026-34076?
@clerk/backend(npm) (versions >= 3.0.0, <= 3.2.2)@clerk/express(npm) (versions >= 2.0.0, <= 2.0.6)@clerk/hono(npm) (versions >= 0.1.0, <= 0.1.4)@clerk/fastify(npm) (versions >= 3.1.0, <= 3.1.4)
- Is there a fix for CVE-2026-34076? Yes. CVE-2026-34076 is fixed in 3.2.3, 2.0.7, 0.1.5, 3.1.5. Upgrade to this version or later.
- Is CVE-2026-34076 exploitable, and should I be worried? Whether CVE-2026-34076 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-34076 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-34076?
- Upgrade
@clerk/backendto 3.2.3 or later - Upgrade
@clerk/expressto 2.0.7 or later - Upgrade
@clerk/honoto 0.1.5 or later - Upgrade
@clerk/fastifyto 3.1.5 or later
- Upgrade