CVE-2026-84394
Description
A flaw was found in fast-uri. The library incorrectly processes Uniform Resource Identifier (URI) hosts containing unbalanced brackets, leading to a discrepancy in how the host is parsed by fast-uri compared to other HTTP clients. This host confusion can allow an attacker to bypass security policies, such as Server-Side Request Forgery (SSRF) denylists or redirect allowlists, by causing an application to evaluate its policy against an incorrect host string. This could result in unintended network requests or access to unauthorized resources.
Statement
This issue is rated Moderate because successful exploitation requires a specific configuration where fast-uri handles security checks but a different client resolves the URL, enabling security policy bypasses without direct code execution. This affects fast-uri versions 2.4.5, 3.1.6, and 4.1.3 (fixed in 2.4.6, 3.1.7, and 4.1.4).
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 7.5 | N/A | 7.5 |
| Attack Vector | Network | N/A | Network |
| Attack Complexity | Low | N/A | Low |
| Privileges Required | None | N/A | None |
| User Interaction | None | N/A | None |
| Scope | Unchanged | N/A | Unchanged |
| Confidentiality | None | N/A | None |
| Integrity Impact | High | N/A | High |
| Availability Impact | None | N/A | None |
Vector
Red Hat: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
cve.org: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Understanding the Weakness (CWE)
Other
Technical Impact: Varies by Context
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