CVE-2026-75899 is a high-severity (CVSS 7.5) CWE-174 vulnerability in fast-uri. A fix is available for fast-uri — see the affected versions and patch details below.
fast-uri vulnerable to server-side request forgery via repeated hostname percent-decoding
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-2026-75899.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2026-75899 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 384,534 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 decodes percent escapes in a hostname during parsing and then decodes the parsed hostname a second time during authority recomposition, so a single call to normalize or resolve can turn nested percent-encoded input into a different network destination such as a loopback hostname or address. For example, a doubly encoded host that spells out a loopback name decodes to that live host in one operation, which contradicts RFC 3986 section 2.4 that an implementation must not decode the same string more than once. An application that normalizes or resolves an untrusted HTTP-family URI before outbound routing, redirect validation, or a host-policy check can receive a destination different from the one the original encoded host represented, giving a server-side request forgery and host-policy bypass primitive. This is an incomplete-fix variant of CVE-2026-6322. The affected versions are 2.4.1 up to but not including 2.4.5, 3.1.2 up to but not including 3.1.6, and 4.0.0 up to but not including 4.1.3. The issue is fixed in 2.4.5, 3.1.6, and 4.1.3, which normalize percent escapes once and preserve encoded percent signs. Users should upgrade to a patched version.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | fast-uri | ≥ 2.4.1&&< 2.4.5 | 2.4.5npm install fast-uri@2.4.5 |
| 📦npm | fast-uri | ≥ 3.1.2&&< 3.1.6 | 3.1.6npm install fast-uri@3.1.6 |
| 📦npm | fast-uri | ≥ 4.0.0&&< 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-2026-75899 is resolved across your whole dependency graph.
Workarounds
Restrict outbound requests from the affected component to an allowlist of hosts, block access to link-local and internal address ranges at the network layer, and require authentication on internal services so a forged request cannot reach them unauthenticated.
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 flaw in the `fast-uri` library, used by applications for URI parsing, allows for Server-Side Request Forgery (SSRF) and host-policy bypass. By crafting a doubly percent-encoded hostname in an untrusted HTTP-family URI, an attacker could redirect internal application requests to arbitrary network destinations,…
Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability.Source: Red Hat security advisory for CVE-2026-75899 (CC BY 4.0)
| Product | Fixed in | Advisory |
|---|---|---|
| Red Hat Enterprise Linux 10 | cockpit-image-builder-0:94.4-1.el10_2 | RHSA-2026:71543 |
| 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 |
Frequently Asked Questions
Is CVE-2026-75899 in your dependencies?
Find it across npm, including transitive dependencies.