In Apache SpamAssassin before 3.4.5, malicious rule configuration (.cf) files can be configured to run system commands without any output or errors. With this, exploits can be injected in a number of scenarios. In addition to upgrading to SA version 3.4.5, users should only use update channels or 3rd party .cf files from trusted places.
Credits
Apache SpamAssassin would like to thank Damian Lukowski at credativ for ethically reporting this issue.
