Fastify vulnerable to invalid content-type parsing, which could lead to validation bypassGHSA-mg2h-6x62-wpwc
HIGHFix: fastify/fastify@436da4cGHSA-mg2h-6x62-wpwc is a high-severity (CVSS 7.5) CWE-1287 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 assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- 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-mg2h-6x62-wpwc.
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
In applications that specify different validation strategies for different content types, it's possible to bypass the validation by providing a slightly altered content type such as with different casing or altered whitespacing before ;.
Users using the the following pattern are affected:
fastify.post('/', {
handler(request, reply) {
reply.code(200).send(request.body)
},
schema: {
body: {
content: {
'application/json': {
schema: {
type: 'object',
properties: {
'foo': {
type: 'string',
}
},
required: ['foo']
}
},
}
}
}
})
User using the following pattern are not affected:
fastify.post('/', {
handler(request, reply) {
reply.code(200).send(request.body)
},
schema: {
body: {
type: 'object',
properties: {
'foo': {
type: 'string',
}
},
required: ['foo']
}
}
})
Patches
This was patched in v5.3.1, but unfortunately it did not cover all problems. This has been fully patched in v5.3.2. Version v4.9.0 was also affected by this issue. This has been fully patched in v4.9.1.
Workarounds
Do not specify multiple content types in the schema.
References
Are there any links users can visit to find out more?
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | fastify | ≥ 5.0.0&&< 5.3.2 | 5.3.2npm install fastify@5.3.2 |
| 📦npm | fastify | ≥ 4.29.0&&< 4.29.1 | 4.29.1npm install fastify@4.29.1 |
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 5.3.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-mg2h-6x62-wpwc 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.
None of the Red Hat Products and Services are impacted by this vulnerability.
To mitigate this vulnerability, do not specify multiple content types in the schema.Source: Red Hat security advisory for GHSA-mg2h-6x62-wpwc (CC BY 4.0)
Frequently Asked Questions
Is GHSA-mg2h-6x62-wpwc in your dependencies?
Find it across npm, including transitive dependencies.