A seven-year old vulnerability in Samba—an open-source implementation of the SMB protocol used by Windows for file and printer sharing—was patched last May but continues to be exploited. According to a security advisory released by the company, the vulnerability allows a malicious actor to upload a shared library to a writable share, causing the server to load and execute it. If leveraged successfully, an attacker could open a command shell in a vulnerable device and take control of it. It affects all versions of Samba since 3.5.0.

http://blog.trendmicro.com/trendlabs-security-intelligence/linux-users-urged-update-new-threat-exploits-sambacry/