GHSA-rfq3-w54c-f9q5 is a medium-severity (CVSS 6.1) Improper Input Validation vulnerability in github.com/ory/fosite. O3 Security confirms whether GHSA-rfq3-w54c-f9q5 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
OAuth2 Redirect URL validity does not respect query parameters and character casing for loopback addresses
Real-World Exposure
github.com/ory/fositeReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.
Description
Impact
fosite#400 (released as v0.30.2) introduced a new feature for handling redirect URLs pointing to loopback interfaces (rfc8252#section-7.3). As part of that change new behavior was introduced which failed to respect the redirect URL's (only for loopback interfaces!) query parameters
- Registering a client with allowed redirect URL
http://127.0.0.1/callback - Performing OAuth2 flow and requesting redirect URL
http://127.0.0.1/callback?bar=foo - Instead of an error, the browser is redirected to
http://127.0.0.1/callback?bar=foowith a potentially successful OAuth2 response.
as well as the host parameter (as long as the host is a loopback interface):
- Registering a client with allowed redirect URL
https://example.com/callback - Performing OAuth2 flow and requesting redirect URL
http://127.0.0.1/callback - Instead of an error, the browser is redirected to
http://127.0.0.1/callbackwith a potentially successful OAuth2 response.
These bugs are only applicable in scenarios where the attacker has control over the loopback interface (localhost, 127.0.0.1, [::1]) where the browser performing the OAuth2 flow is running.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/ory/fosite | ≥ 0.30.3&&< 0.34.1 | 0.34.1 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/ory/fosite. 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 github.com/ory/fosite to 0.34.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-rfq3-w54c-f9q5 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-rfq3-w54c-f9q5 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-rfq3-w54c-f9q5. 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-rfq3-w54c-f9q5 in your dependencies?
O3 detects GHSA-rfq3-w54c-f9q5 across Go dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.