CVE-2026-18446 — fast-uri
HIGHCVE-2026-18446 is a high-severity (CVSS 7.5) CWE-436 vulnerability in fast-uri. A fix is available for fast-uri — see the affected versions and patch details below.
fast-uri vulnerable to host confusion via backslash authority introducer
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 CVE-2026-18446.
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
CVE-2026-18446 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 374,847 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
fast-uri before 4.1.2, 3.1.5, and 2.4.4 requires a literal double forward slash to recognize a URI authority, so a reference that uses a backslash based introducer in place of it (backslash backslash, forward slash backslash, or backslash forward slash) is parsed with no authority and folds into the path. Node's native WHATWG URL parser instead treats a backslash as interchangeable with a forward slash for special schemes, so the two parsers extract different hosts from the same input. Applications that use fast-uri to enforce host based policy such as allowlists, SSRF filtering, or redirect validation before passing the same URL into Node's URL or fetch consumers can be steered to an unintended host. Upgrade to fast-uri 4.1.2, 3.1.5, or 2.4.4.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | fast-uri | all versions | 2.4.4npm install fast-uri@2.4.4 |
| 📦npm | fast-uri | ≥ 3.0.0&&< 3.1.5 | 3.1.5npm install fast-uri@3.1.5 |
| 📦npm | fast-uri | ≥ 4.0.0&&< 4.1.2 | 4.1.2npm install fast-uri@4.1.2 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for fast-uri, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update fast-uri to 2.4.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-18446 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 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-18446 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-18446. 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.
This is an Important host confusion vulnerability in fast-uri, which can affect Red Hat products that use the library for URI parsing and security policy enforcement. The discrepancy in how fast-uri handles backslash-based URI authority introducers compared to Node.js's native URL parser can lead to bypasses of…
| Product | Fixed in | Advisory |
|---|---|---|
| Red Hat Hardened Images | grafana13-1-main-13.1.1-0.4.hum1 | RHSA-2026:49387 |
| Red Hat Hardened Images | grafana12-4-main-12.4.6-0.3.hum1 | RHSA-2026:49401 |
| Red Hat OpenShift Container Platform 4.16 | openshift4/ose-monitoring-plugin-rhel9:1788235712 | RHSA-2026:62550 |
Frequently Asked Questions
Is CVE-2026-18446 in your dependencies?
O3 Security finds CVE-2026-18446 across npm dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.