GHSA-3vhc-576x-3qv4 is a high-severity (CVSS 8.2) CWE-347 vulnerability in hono. A fix is available for hono — see the affected versions and patch details below.
Hono JWK Auth Middleware has JWT algorithm confusion when JWK lacks "alg" (untrusted header.alg fallback)
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-3vhc-576x-3qv4.
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-3vhc-576x-3qv4 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 378,567 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.
hononpmDescription
Summary
A flaw in Hono’s JWK/JWKS JWT verification middleware allowed the algorithm specified in the JWT header to influence signature verification when the selected JWK did not explicitly define an algorithm. This could enable JWT algorithm confusion and, in certain configurations, allow forged tokens to be accepted.
Details
When verifying JWTs using JWKs or a JWKS endpoint, the middleware selected the verification algorithm based on the JWK’s alg field if present. If the JWK did not specify an algorithm, the middleware fell back to using the alg value provided in the unverified JWT header.
Because the alg field in a JWK is optional and commonly omitted in real-world JWKS configurations, this behavior could allow an attacker to influence which algorithm is used for verification. In some environments, this may result in authentication or authorization bypass through crafted JWTs.
The practical impact depends on application configuration, including which algorithms are accepted and how JWTs are used to make authorization decisions.
Impact
In affected configurations, an attacker may be able to forge JWTs with attacker-controlled claims, potentially leading to authentication or authorization bypass.
Applications that do not use the JWK/JWKS middleware, do not rely on JWT-based authentication, or explicitly restrict allowed algorithms are not affected.
Resolution
Update to the latest patched release.
Breaking change:
The JWK/JWKS JWT verification middleware has been updated to require an explicit allowlist of asymmetric algorithms when verifying tokens. The middleware no longer derives the verification algorithm from untrusted JWT header values.
Instead, callers must explicitly specify which asymmetric algorithms are permitted, and only tokens signed with those algorithms will be accepted. This prevents JWT algorithm confusion by ensuring that algorithm selection is fully controlled by application configuration.
As part of this fix, the alg option is now required when using the JWK/JWKS middleware, and symmetric (HS*) algorithms are no longer accepted in this context.
Before (vulnerable configuration)
import { jwk } from 'hono/jwk'
app.use(
'/auth/*',
jwk({
jwks_uri: 'https://example.com/.well-known/jwks.json',
// alg was optional
})
)
After (patched configuration)
import { jwk } from 'hono/jwk'
app.use(
'/auth/*',
jwk({
jwks_uri: 'https://example.com/.well-known/jwks.json',
alg: ['RS256'], // required: explicit asymmetric algorithm allowlist
})
)
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | hono | all versions | 4.11.4npm install hono@4.11.4 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for hono, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update hono to 4.11.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-3vhc-576x-3qv4 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-3vhc-576x-3qv4 can be triaged on real exposure rather than presence alone.
Tailored to GHSA-3vhc-576x-3qv4. 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-3vhc-576x-3qv4 in your dependencies?
O3 Security finds GHSA-3vhc-576x-3qv4 across npm dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.