CVE-2026-33808
9.1 · CRITICALOverview
CVE-2026-33808 is a critical-severity vulnerability affecting fastify fastify\/express. It was published on April 15, 2026 and has a CVSS 3.1 base score of 9.1 (CRITICAL).
This vulnerability has a CVSS 3.1 base score of 9.1, rated CRITICAL. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.
Technical Description
Impact@fastify/express v4.0.4 and earlier fails to normalize URLs before passing them to Express middleware when Fastify router normalization options are enabled. This allows complete bypass of path-scoped authentication middleware via duplicate slashes when ignoreDuplicateSlashes is enabled, or via semicolon delimiters when useSemicolonDelimiter is enabled. In both cases, Fastify router normalizes the URL and matches the route, but @fastify/express passes the original un-normalized URL to Express middleware, which fails to match and is skipped. An unauthenticated attacker can access protected routes by manipulating the URL path.
PatchesUpgrade to @fastify/express v4.0.5 or later.
Remediation
Check the references section for vendor advisories and patches from fastify. Update fastify\/express to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.
Affected Products
| Vendor | Product | Versions | Status |
|---|---|---|---|
| fastify | fastify\/express | >= 0, < 4.0.5 | Affected |
Frequently Asked Questions
What is CVE-2026-33808?
CVE-2026-33808 is a critical-severity vulnerability affecting fastify fastify\/express. It was published on April 15, 2026 and has a CVSS 3.1 base score of 9.1 (CRITICAL).
How severe is CVE-2026-33808?
This vulnerability has a CVSS 3.1 base score of 9.1, rated CRITICAL. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.
How do I fix or remediate CVE-2026-33808?
Check the references section for vendor advisories and patches from fastify. Update fastify\/express to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.
How can CyberStrike help with CVE-2026-33808?
CyberStrike's AI-powered security agents can automatically detect CVE-2026-33808 across your infrastructure using autonomous pentesting, DAST scanning, and HackBrowser. The platform continuously monitors for known vulnerabilities and provides actionable remediation guidance prioritized by real-world exploitability.
How CyberStrike Helps
AI agents map your attack surface to find vulnerabilities like this one.
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