CVE-2026-75931 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 skipped IDN canonicalization on scheme-relative references
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-2026-75931.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2026-75931 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 384,993 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
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 is a URI parser for Node.js. It canonicalizes a host to its ASCII form only when the input carries an explicit scheme, so a scheme-relative reference such as a host preceded by two slashes is returned with its host verbatim and no error set. As a result fast-uri's own entry points disagree with each other: parse, resolve, normalize, and equal can yield different hosts for the same input depending only on whether a scheme is written out, and equal can return opposite verdicts for the same pair of hosts. An application that extracts a host with fast-uri to check it against a policy list and then resolves the same reference can make its decision on one host while the destination is another, enabling host confusion and policy bypass. The affected versions are 2.4.2 up to but not including 2.4.5, 3.1.3 up to but not including 3.1.6, and 4.0.1 up to but not including 4.1.3. The issue is fixed in 2.4.5, 3.1.6, and 4.1.3, which canonicalize the host consistently across the resolve path. Users should upgrade to a patched version.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | fast-uri | ≥ 2.4.2&&< 2.4.5 | 2.4.5npm install fast-uri@2.4.5 |
| 📦npm | fast-uri | ≥ 3.1.3&&< 3.1.6 | 3.1.6npm install fast-uri@3.1.6 |
| 📦npm | fast-uri | ≥ 4.0.1&&< 4.1.3 | 4.1.3npm install fast-uri@4.1.3 |
Affected Products
fast-uriopenjsfDetection & 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 2.4.5 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-75931 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.
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.
| Product | Fixed in | Advisory |
|---|---|---|
| Red Hat Satellite 6.19 for RHEL 9 | foreman-0:3.18.0.14-1.el9sat | RHSA-2026:74503 |
| Cluster Observability Operator 1.5.3 | cluster-observability-operator/troubleshooting-panel-console-plugin-rhel9:1790854494 | RHSA-2026:74609 |
| multicluster engine for Kubernetes 2.11 | multicluster-engine/console-mce-rhel9:1790133081 | RHSA-2026:72848 |
| multicluster engine for Kubernetes 2.17 | multicluster-engine/console-mce-rhel9:1790135323 | RHSA-2026:72849 |
| Network Observability (NETOBSERV) 1.12.3 | network-observability/network-observability-console-plugin-pf5-rhel9:1789978780 | RHSA-2026:70593 |
| Red Hat Advanced Cluster Management for Kubernetes 2.16 | rhacm2/console-rhel9:1788880980 | RHSA-2026:67542 |
| Red Hat Advanced Cluster Management for Kubernetes 2.16 | rhacm2/console-rhel9:1788283612 | RHSA-2026:72880 |
| Red Hat Advanced Cluster Management for Kubernetes 2.17 | rhacm2/console-rhel9:1788883472 | RHSA-2026:67543 |
Frequently Asked Questions
Is CVE-2026-75931 in your dependencies?
Find it across npm, including transitive dependencies.