Lychee is a free, open-source photo-management tool. Prior to version 6.6.13, a critical Server-Side Request Forgery (SSRF) vulnerability exists in the /api/v2/Photo::fromUrl endpoint. This flaw lets an attacker instruct the application’s backend to make HTTP requests to any URL they choose. Consequently, internal network resources—such as localhost services or cloud-provider metadata endpoints—become reachable. The endpoint takes a URL from the user and calls it server-side via fopen() without any safeguards. There is no IP address validation, nor are there any allow-list, timeout, or size restrictions. Because of this, attackers can point the application at internal targets. Using this flaw, an attacker can perform internal port scans or retrieve sensitive cloud metadata. Version 6.6.13 contains a patch for the issue.
The web server receives a URL or similar request from an upstream component and retrieves the contents of this URL, but it does not sufficiently ensure that the request is being sent to the expected destination.