GHSA-qmw8-3v4g-gwj4 is a critical-severity (CVSS 10) Improper Input Validation vulnerability in fastify-reply-from. O3 Security confirms whether GHSA-qmw8-3v4g-gwj4 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Prefix escape
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.
fastify-reply-fromnpmDescription
Impact
By crafting a specific URL, it is possible to escape the prefix of the proxied backend service.
If the base url of the proxied server is /pub/, a user expect that accessing /priv on the target service would not be possible. Unfortunately, it is.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N
Patches
A patch have been submitted by Corey Farrell [email protected], the reporter. All releases after v4.0.2 include the fix.
Workarounds
There are no workaround available.
For more information
If you have any questions or comments about this advisory:
- Open an issue in fastify-reply-from
- Email us at [email protected]
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | fastify-reply-from | all versions | 4.0.2 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for fastify-reply-from. 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-reply-from to 4.0.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-qmw8-3v4g-gwj4 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-qmw8-3v4g-gwj4 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-qmw8-3v4g-gwj4. 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-qmw8-3v4g-gwj4 in your dependencies?
O3 detects GHSA-qmw8-3v4g-gwj4 across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.