Details
Critical Description
This issue was initially reported to the security team by Alvaro Munoz <pwntester@github.com> from the GitHub Security Lab team <securitylab@github.com>. It was also reported 15 days later by Kai Zhao <happyhacking@outlook.it>.
It's a well known post-auth vulnerability[1][2][3] so no CVE was created. It relies on Freemarker freemarker.template.utility.Execute class and new() built-in.
Since Freemarker 2.3.17 a known solution to these issues is to register a TemplateClassResolver in Freemarker configuration in order to limit which TemplateModels can be instantiated in the templates. The predefined resolver SAFER_RESOLVER doesn't allow to instantiate the Execute class[4]. So the solution is to add the line
newConfig.setNewBuiltinClassResolver(TemplateClassResolver.SAFER_RESOLVER);
in FreeMarkerWorker.java
In [1] a concern about the Freemarker api buit-in is mentioned. Actually this is not a concern by default in Freemarker[5] and OFBiz
The api_builtin_enabled configuration setting must be set to true. Its default is false (at least as of 2.3.22) for not lowering the security of existing applications.
[1] https://ackcent.com/blog/in-depth-freemarker-template-injection/
[2] https://insinuator.net/2016/07/dilligent-bug/
[3] https://portswigger.net/research/server-side-template-injection
[4] https://freemarker.apache.org/docs/api/freemarker/core/TemplateClassResolver.html#SAFER_RESOLVER
[5] https://freemarker.apache.org/docs/ref_builtins_expert.html#ref_buitin_api_and_has_api