GHSA-mg2h-6x62-wpwc is a high-severity (CVSS 7.5) CWE-1287 vulnerability in fastify. O3 Security confirms whether GHSA-mg2h-6x62-wpwc is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Fastify vulnerable to invalid content-type parsing, which could lead to validation bypass
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, a proxy for how much of the ecosystem is exposed.
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 | 5.3.2 |
| 📦npm | fastify | ≥ 4.29.0&&< 4.29.1 | 4.29.1 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for fastify. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
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.
How O3 protects you
O3 pinpoints whether GHSA-mg2h-6x62-wpwc is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to GHSA-mg2h-6x62-wpwc. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-mg2h-6x62-wpwc in your dependencies?
O3 detects GHSA-mg2h-6x62-wpwc across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.