A Server-Side Request Forgery (SSRF) vulnerability in the /Upgrade/FixConfig route in Open Library Foundation VuFind 2.0 through 9.1 before 9.1.1 allows a remote attacker to overwrite local configuration files to gain access to the administrator panel and achieve Remote Code Execution. A mitigating factor is that it requires the allow_url_include PHP runtime setting to be on, which is off in default installations. It also requires the /Upgrade route to be exposed, which is exposed by default after installing VuFind, and is recommended to be disabled by setting autoConfigure to false in config.ini.
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.