GHSA-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.
Fastify vulnerable to invalid content-type parsing, which could lead to validation bypass
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
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
GHSA-mg2h-6x62-wpwc plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 379,145 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
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 |
Detection & 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.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like GHSA-mg2h-6x62-wpwc can be triaged on real exposure rather than presence alone.
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 Security finds GHSA-mg2h-6x62-wpwc across npm dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.