Crowd and Crowd Data Center had the pdkinstall development plugin incorrectly enabled in release builds. Attackers who can send unauthenticated or authenticated requests to a Crowd or Crowd Data Center instance can exploit this vulnerability to install arbitrary plugins, which permits remote code execution on systems running a vulnerable version of Crowd or Crowd Data Center.

Affected versions:

• All versions of Crowd from version 2.1.0 before 3.0.5 (the fixed version for 3.0.x), from version 3.1.0 before 3.1.6 (the fixed version for 3.1.x), from version 3.2.0 before 3.2.8 (the fixed version for 3.2.x), from version 3.3.0 before 3.3.5 (the fixed version for 3.3.x), and from version 3.4.0 before 3.4.4 (the fixed version for 3.4.x) are affected by this vulnerability.

Fix:

• Crowd and Crowd Data Center version 3.4.4 is available for download from https://www.atlassian.com/software/crowd/download
• Crowd and Crowd Data Center versions 3.0.5, 3.1.6, 3.2.8, and 3.3.5 are available for download from https://www.atlassian.com/software/crowd/download-archive

 
Mitigation

Atlassian recommends that you upgrade to the latest version. However, this issue can be mitigated as per the following instructions:

1. Stop Crowd
2. Find and delete any pdkinstall-plugin jar files from the Crowd installation directory and the data directory
3. Remove the pdkinstall-plugin jar file from <Crowd installation directory>/crowd-webapp/WEB-INF/classes/atlassian-bundled-plugins.zip
4. Start Crowd
5. Check that there are no pdkinstall-plugin jar files in the installation directory or the data directory. 

For additional details, see the full advisory.