Fastify: Incorrect Content-Type parsing can lead to CSRF attackGHSA-3fjj-p79j-c9hh
MEDIUMFix: fastify/fastify@62dde76GHSA-3fjj-p79j-c9hh is a medium-severity (CVSS 4.2) Cross-Site Request Forgery (CSRF) vulnerability in fastify. A fix is available for fastify — see the affected versions and patch details below.
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for GHSA-3fjj-p79j-c9hh.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.
fastifynpmDescription
Impact
The attacker can use the incorrect Content-Type to bypass the Pre-Flight checking of fetch. fetch() requests with Content-Type’s essence as "application/x-www-form-urlencoded", "multipart/form-data", or "text/plain", could potentially be used to invoke routes that only accepts application/json content type, thus bypassing any CORS protection, and therefore they could lead to a Cross-Site Request Forgery attack.
Patches
For 4.x users, please update to at least 4.10.2
For 3.x users, please update to at least 3.29.4
Workarounds
Implement Cross-Site Request Forgery protection using @fastify/csrf.
References
Check out the HackerOne report: https://hackerone.com/reports/1763832.
For more information
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | fastify | ≥ 4.0.0&&< 4.10.2 | 4.10.2npm install fastify@4.10.2 |
| 📦npm | fastify | ≥ 3.0.0&&< 3.29.4 | 3.29.4npm install fastify@3.29.4 |
Affected Products
fastifyfastifyDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for fastify, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update fastify to 4.10.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-3fjj-p79j-c9hh is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
Implement Cross-site request forgery protection using `@fastify/csrf'.Source: Red Hat security advisory for GHSA-3fjj-p79j-c9hh (CC BY 4.0)
Frequently Asked Questions
Is GHSA-3fjj-p79j-c9hh in your dependencies?
Find it across npm, including transitive dependencies.