New Linux malware hides in cron jobs with invalid dates

LASER_oneXM

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Security researchers have discovered a new remote access trojan (RAT) for Linux that keeps an almost invisible profile by hiding in tasks scheduled for execution on a non-existent day, February 31st.

Dubbed CronRAT, the malware is currently targeting web stores and enables attackers to steal credit card data by deploying online payment skimmers on Linux servers.
Characterized by both ingenuity and sophistication, as far as malware for online stores is concerned, CronRAT is undetected by many antivirus engines.

Clever hideout for payloads​

CronRAT abuses the Linux task scheduling system, cron, which allows scheduling tasks to run on non-existent days of the calendar, such as February 31st.
The Linux cron system accepts date specifications as long as they have a valid format, even if the day does not exist in the calendar - which means that the scheduled task won’t execute.

This is what CronRAT relies on to achieve its stealth. A report today from Dutch cyber-security company Sansec explains that it hides a “sophisticated Bash program” in the names of the scheduled tasks.