Interpretation Conflict in fast-uri - CVE-2026-16221
Published: July 22, 2026
Vulnerability identifier: #VU139081
CSH Severity: Medium
CVSS v4: 8.7 [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]
CVE-ID: CVE-2026-16221
CWE-ID: CWE-436
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote attacker to bypass host-based policy checks and route requests to an unintended destination.
The vulnerability exists due to interpretation conflict in the fast-uri URL parser when parsing URLs containing a literal backslash in the authority section for special schemes. A remote attacker can supply a specially crafted URL to bypass host-based policy checks and route requests to an unintended destination.
This issue can occur when an application validates a URL with fast-uri and then passes the same input to Node's WHATWG URL parser or fetch-related consumers, which extract a different host from the same string.
Affected software
fast-uri
Bitbucket Data Center
Bamboo Data Center
Bitbucket Data Center
Bamboo Data Center
How to mitigate CVE-2026-16221
Install security update from vendor's website.
fast-uri - addressed in versions 2.4.3, 3.1.4, 4.1.1
Bitbucket Data Center - update to 9.4.23
Bamboo Data Center - update to 10.2.22
Bitbucket Data Center - update to 9.4.23
Bamboo Data Center - update to 10.2.22