Shelf Vulnerable to Server-Side Request Forgery (SSRF) via Asset CSV Import imageUrl Validation Bypass

Shelf is a platform for tracking physical assets. Prior to version 1.20.3, authenticated users with the `asset:import` permission can trigger server-side HTTP requests to attacker-controlled URLs through the Asset CSV Content Import feature. The `imageUrl` validation logic can be bypassed through multiple techniques, including image-extension suffixes, image-related path keywords, domain substring matching, and redirect chains. After validation, the server performs an unrestricted `fetch()` request to the supplied URL. This results in a Server-Side Request Forgery (SSRF) vulnerability that allows attackers to reach internal network services, cloud metadata endpoints, and arbitrary external hosts from the application's network context. Additionally, response bodies are fully buffered before size validation, creating a potential memory exhaustion vector. Version 1.20.3 patches the issue.