Double Decoding of the Same Data in fast-uri - CVE-2026-75899
Published: August 25, 2026
Vulnerability identifier: #VU145068
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-2026-75899
CWE-ID: CWE-174
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote attacker to perform server-side request forgery.
The vulnerability exists due to double decoding of the same data in the fast-uri normalize() and resolve() hostname handling logic when processing a URI with a nested percent-encoded host. A remote attacker can supply a specially crafted URI to perform server-side request forgery.
The issue can cause the hostname to be interpreted as a different destination than the input appears to contain, including internal addresses such as loopback or a cloud metadata endpoint.
Affected software
fast-uri
How to mitigate CVE-2026-75899
Install security update from vendor's website.
fast-uri - addressed in versions 2.4.5, 3.1.6, 4.1.3