Description
Apache Solr 5.0.0 to Apache Solr 8.3.1 are vulnerable to a Remote Code Execution through the VelocityResponseWriter. A Velocity template can be provided through Velocity templates in a configset `velocity/` directory or as a parameter. A user defined configset could contain renderable, potentially malicious, templates. Parameter provided templates are disabled by default, but can be enabled by setting `params.resource.loader.enabled` by defining a response writer with that setting set to `true`. Defining a response writer requires configuration API access. Solr 8.4 removed the params resource loader entirely, and only enables the configset-provided template rendering when the configset is `trusted` (has been uploaded by an authenticated user).
Remediation
References
https://issues.apache.org/jira/browse/SOLR-13971
http://packetstormsecurity.com/files/157078/Apache-Solr-8.3.0-Velocity-Template-Remote-Code-Execution.html
https://www.oracle.com/security-alerts/cpuoct2020.html
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