GHSA-v2hh-gcrm-f6hx is a high-severity (CVSS 7.5) CWE-436 vulnerability in fast-uri. O3 Security confirms whether GHSA-v2hh-gcrm-f6hx is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
fast-uri vulnerable to host confusion via literal backslash authority delimiter
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-v2hh-gcrm-f6hx.
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-v2hh-gcrm-f6hx 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 367,996 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.
fast-urinpmDescription
Impact
fast-uri v4.1.0 and earlier do not treat a literal backslash (U+005C) as an authority delimiter. Node's native WHATWG URL (used by fetch(), undici, and Node's http/https clients) normalizes \ to / for special schemes (http, https, ws, wss, ftp, file), so the two parsers extract different hosts from the same input string.
For example, http://evil.com\@allowed.com is treated by fast-uri as host allowed.com with userinfo evil.com\, while Node's WHATWG URL parser and fetch() see host evil.com with path /@allowed.com.
Applications that use fast-uri to enforce host-based policy (allowlists, denylists, loopback/SSRF filtering, redirect validation, outbound proxy routing) before passing the same URL into Node's URL or fetch() consumers see a policy/use desync and can be steered to an unintended destination, including cloud metadata endpoints, loopback, or internal hosts.
Patches
Upgrade to fast-uri v4.1.1, v3.1.4, or v2.4.3.
Workarounds
None. Upgrade to the patched version.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | fast-uri | ≥ 2.3.1&&< 2.4.3 | 2.4.3 |
| 📦npm | fast-uri | ≥ 3.0.0&&< 3.1.4 | 3.1.4 |
| 📦npm | fast-uri | ≥ 4.0.0&&< 4.1.1 | 4.1.1 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for fast-uri. 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 fast-uri to 2.4.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-v2hh-gcrm-f6hx 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-v2hh-gcrm-f6hx 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-v2hh-gcrm-f6hx. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
Important: This flaw in fast-uri allows for a security policy bypass due to inconsistent URL parsing between fast-uri and Node.js's native WHATWG URL parser. Applications within Red Hat Hardened Images that rely on fast-uri for host-based policy enforcement, such as allowlists or Server-Side Request Forgery (SSRF)…
Frequently Asked Questions
Is GHSA-v2hh-gcrm-f6hx in your dependencies?
O3 detects GHSA-v2hh-gcrm-f6hx across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.