Interpretation Conflict in fast-uri - CVE-2026-13676
Published: July 21, 2026
Vulnerability identifier: #VU138918
CSH Severity: High
CVSS v4.0: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/E:U/U:Amber
CVE-ID: CVE-2026-13676
CWE-ID: CWE-436
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vendor: fastify.io
Affected software:
fast-uri
fast-uri
Detailed vulnerability description
The vulnerability allows a remote attacker to modify data on the system.
The vulnerability exists due to fast-uri fail to canonicalize Unicode (IDN) hostnames for HTTP-family URLs. The IDN conversion path calls a helper that does not exist on the global URL constructor, silently leaving the host in its original Unicode form while normalize() and equal() still return values that differ from a WHATWG-compatible URL parser. A remote attacker can trigger the vulnerability to modify data on the system.
How to mitigate CVE-2026-13676
Install updates from vendor's website.
Sources
- https://cna.openjsf.org/security-advisories.html
- https://github.com/fastify/fast-uri/security/advisories/GHSA-4c8g-83qw-93j6
- https://access.redhat.com/errata/RHSA-2026:37186
- https://access.redhat.com/errata/RHSA-2026:37585
- https://access.redhat.com/errata/RHSA-2026:37628
- https://access.redhat.com/errata/RHSA-2026:40118
- https://access.redhat.com/errata/RHSA-2026:40262
- https://access.redhat.com/errata/RHSA-2026:40945
- https://access.redhat.com/errata/RHSA-2026:41066
- https://access.redhat.com/security/cve/CVE-2026-13676
- https://bugzilla.redhat.com/show_bug.cgi?id=2494197
- https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-13676.json