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.
Blast Radius
Weekly download volume for affected packages — a proxy for how broadly this vulnerability is deployed.
h3npmDescription
I was digging into h3 v1 (specifically v1.15.4) and found a critical HTTP Request Smuggling vulnerability.
Basically, readRawBody is doing a strict case-sensitive check for the Transfer-Encoding header. It explicitly looks for "chunked", but per the RFC, this header should be case-insensitive.
The Bug: If I send a request with Transfer-Encoding: ChuNked (mixed case), h3 misses it. Since it doesn't see "chunked" and there's no Content-Length, it assumes the body is empty and processes the request immediately.
This leaves the actual body sitting on the socket, which triggers a classic TE.TE Desync (Request Smuggling) if the app is running behind a Layer 4 proxy or anything that doesn't normalize headers (like AWS NLB or Node proxies).
Vulnerable Code (src/utils/body.ts):
if (
!Number.parseInt(event.node.req.headers["content-length"] || "") &&
!String(event.node.req.headers["transfer-encoding"] ?? "")
.split(",")
.map((e) => e.trim())
.filter(Boolean)
.includes("chunked") // <--- This is the issue. "ChuNkEd" returns false here.
) {
return Promise.resolve(undefined);
}
I verified this locally:
- Sent a
Transfer-Encoding: ChunKedrequest without a closing 0 chunk. - Express hangs (correctly waiting for data).
- h3 responds immediately (vulnerable, thinks body is length 0).
Impact: Since H3/Nuxt/Nitro is often used in containerized setups behind TCP load balancers, an attacker can use this to smuggle requests past WAFs or desynchronize the socket to poison other users' connections.
Fix: Just need to normalize the header value before checking: .map((e) => e.trim().toLowerCase())
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | h3 | all versions | 1.15.5 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for h3. 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 h3 to 1.15.5 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-mp2g-9vg9-f4cg 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-mp2g-9vg9-f4cg 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-mp2g-9vg9-f4cg. 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-mp2g-9vg9-f4cg in your dependencies?
O3 detects GHSA-mp2g-9vg9-f4cg across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.