GoCD is a continuous deliver server. GoCD versions prior to 24.4.0 can allow GoCD group admins to abuse ability to edit the raw XML configuration for groups they administer to trigger XML External Entity (XXE) injection on the GoCD server. Theoretically, the XXE vulnerability can result in additional attacks such as SSRF, information disclosure from the GoCD server, and directory traversal, although these additional attacks have not been explicitly demonstrated as exploitable. This issue is fixed in GoCD 24.5.0. Some workarounds are available. One may temporarily block access to /go/*/pipelines/snippet routes from an external reverse proxy or WAF if ones group admin users do not need the functionality to edit the XML of pipelines directly (rather than using the UI, or using a configuration repository). One may also prevent external access from ones GoCD server to arbitrary locations using some kind of environment egress control.
The product processes an XML document that can contain XML entities with URIs that resolve to documents outside of the intended sphere of control, causing the product to embed incorrect documents into its output.
XML documents optionally contain a Document Type Definition (DTD), which, among other features, enables the definition of XML entities. It is possible to define an entity by providing a substitution string in the form of a URI. The XML parser can access the contents of this URI and embed these contents back into the XML document for further processing. By submitting an XML file that defines an external entity with a file:// URI, an attacker can cause the processing application to read the contents of a local file. For example, a URI such as “file:///c:/winnt/win.ini” designates (in Windows) the file C:\Winnt\win.ini, or file:///etc/passwd designates the password file in Unix-based systems. Using URIs with other schemes such as http://, the attacker can force the application to make outgoing requests to servers that the attacker cannot reach directly, which can be used to bypass firewall restrictions or hide the source of attacks such as port scanning. Once the content of the URI is read, it is fed back into the application that is processing the XML. This application may echo back the data (e.g. in an error message), thereby exposing the file contents.