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CVE-2026-13676 fast-uri CVE debrief

The fast-uri library, used for parsing URLs in Node.js applications, has a vulnerability that allows bypassing of host-based security policies. Specifically, fast-uri versions 2.3.1 through 3.1.2 and 4.0.0 do not properly canonicalize Unicode (IDN) hostnames for HTTP-family URLs. This can lead to security issues when applications use fast-uri to enforce host-based policies such as denylists, loopback filtering, redirect validation, and outbound proxy routing before passing the URL to Node's URL or fetch APIs.

Vendor
fast-uri
Product
Unknown
CVSS
HIGH 7.5
CISA KEV
Not listed in stored evidence
Original CVE published
2026-06-29
Original CVE updated
2026-07-10
Advisory published
2026-06-29
Advisory updated
2026-07-10

Who should care

Developers and security teams using fast-uri in Node.js applications, especially those enforcing host-based security policies, should be aware of this vulnerability. Applications that rely on fast-uri for URL parsing and policy enforcement are potentially affected.

Technical summary

The vulnerability in fast-uri arises from its failure to properly canonicalize Unicode (IDN) hostnames for HTTP-family URLs. This means that when an application uses fast-uri to parse a URL with a Unicode hostname, it may not correctly resolve to the same host as a standard URL parser. This discrepancy can be exploited to bypass host-based security policies. For instance, an attacker could provide a URL with a Unicode hostname that is equivalent to a blocked or restricted hostname according to the application's policies, but is not correctly identified as such by fast-uri. Patches are available in fast-uri versions 3.1.3 for the 3.x line and 4.0.1 for the 4.x line.

Defensive priority

High

Recommended defensive actions

  • Upgrade to fast-uri version 3.1.3 for the 3.x line or 4.0.1 for the 4.x line.
  • Enforce host policy using the same URL parser used for the actual request.
  • Reject non-ASCII hosts before policy checks.
  • Review compensating controls for exposed systems while remediation is scheduled and verified.
  • Check relevant monitoring, detection, and logs for exposed assets that need extra review.
  • Track exceptions, retest remediated assets, and close the item only after evidence is documented.
  • Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up.

Evidence notes

The CVE record was published on 2026-06-29T14:16:47.967Z and was last modified on 2026-07-10T12:16:31.630Z. The NVD entry is currently Analyzed. Evidence is limited to public sources and may not reflect the full scope or impact of the vulnerability. Affected systems and deployments should be verified through independent assessment or vendor guidance. Additional details may be found in vendor advisories or through internal risk assessment processes.

Official resources

AI-assisted PatchSiren debrief based on the supplied source corpus. The CVE record was published on 2026-06-29T14:16:47.967Z and has not been modified since then. The NVD entry is currently Analyzed.