Log4Shell, the critical unauthenticated remote code execution vulnerability identified in early December 2021 in the Apache Log4j logging utility, hasn’t seen the mass exploitation that many expected, but an exploit for it is now part of the Mirai botnet’s arsenal, researchers warn.
Both cybercriminals and nation-state threat actors have been observed exploiting the security bug – which is tracked as CVE-2021-44228 – in their attacks, including in assaults targeting industrial organizations.
Despite that, no mass exploitation of the vulnerability has been observed to date, most likely because the industry jumped into action and took the necessary steps to address or mitigate Log4Shell and the remaining security issues identified in Log4j over the past two months.
“As soon as details of the Log4Shell bug became clear, the world’s biggest and most important cloud services, software packages and enterprises took action to steer away from the iceberg, supported by shared threat intelligence and practical guidance from the security community,” Sophos notes.
Sophos says it saw a peak of Log4Shell scans between Dec. 20 and Dec. 23, 2021 – its applications were hit more than 600,000 per day –, followed by a drop over the next week. The attacks flattened in January 2022, at around 100,000 daily hits on Sophos’ firewalls.
Log4Shell exploitation is different depending on the application that implements Log4j, meaning that threat actors likely performed a large number of redundant scans while attempting to figure out how to exploit each application, Sophos notes.
“This doesn’t mean the threat level declined too: by this time, an ever-greater percentage of detections were likely real attacks, with fewer coming from researchers monitoring the latest patching status,” Sophos says.
With more threat actors adding exploits to their arsenals, exploitation of the Log4j vulnerabilities is expected to continue.
Recently, even malware spreading the Mirai botnet – well known for being used to launch massive distributed denial of service (DDoS) attacks – was observed packing code designed to exploit Log4Shell (CVE-2021-44228), Akamai says.
However, the exploit appears designed to specifically target devices from Zyxel, which has already confirmed impact from the vulnerability.
One of the observed samples was designed to scan for a large number of devices vulnerable to remote code execution, while a second one dropped these functions in favor of Log4j exploitation. The standard Mirai attack functions were still present in it.