CVE-2026-16221
7.5 · HIGHOverview
CVE-2026-16221 is a high-severity vulnerability affecting openjsf fast-uri. It was published on July 19, 2026 and has a CVSS 3.1 base score of 7.5 (HIGH).
This vulnerability has a CVSS 3.1 base score of 7.5, rated HIGH. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.
Technical Description
Impact: fast-uri versions from 2.3.1 through 4.1.0 (including the 3.x line up to 3.1.3 and the 2.x line up to 2.4.2) do not treat a literal backslash character (U+005C) as an authority delimiter. Node's native WHATWG URL parser, used by fetch, undici, and Node's http and https clients, normalizes the backslash to a forward slash for special schemes such as http, https, ws, wss, ftp, and file. As a result, the two parsers extract different hosts from the same input string. Applications that use fast-uri to enforce host-based policy such as allowlists, denylists, loopback or SSRF filtering, redirect validation, or outbound proxy routing before passing the same URL into Node's URL or fetch consumers can be steered to an unintended destination, including cloud metadata endpoints, loopback, or internal hosts.
Patches: upgrade to fast-uri 4.1.1, 3.1.4, or 2.4.3.
Workarounds: none.
Remediation
Check the references section for vendor advisories and patches from openjsf. Update fast-uri to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.
Affected Products
| Vendor | Product | Versions | Status |
|---|---|---|---|
| openjsf | fast-uri | >= 2.3.1, < 2.4.3 | Affected |
Frequently Asked Questions
What is CVE-2026-16221?
CVE-2026-16221 is a high-severity vulnerability affecting openjsf fast-uri. It was published on July 19, 2026 and has a CVSS 3.1 base score of 7.5 (HIGH).
How severe is CVE-2026-16221?
This vulnerability has a CVSS 3.1 base score of 7.5, rated HIGH. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.
How do I fix or remediate CVE-2026-16221?
Check the references section for vendor advisories and patches from openjsf. Update fast-uri to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.
How can CyberStrike help with CVE-2026-16221?
CyberStrike's AI-powered security agents can automatically detect CVE-2026-16221 across your infrastructure using autonomous pentesting, DAST scanning, and HackBrowser. The platform continuously monitors for known vulnerabilities and provides actionable remediation guidance prioritized by real-world exploitability.
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