Dormant Malicious Code Discovered on Thousands of Websites
29 December 2015Here’s the latest from Yuchen Zhou (PhD 2015, now at Palo Alto Networks): Dormant Malicious Code Discovered on Thousands of Websites, Yuchen Zhou and Wei Xu, Palo Alto Networks Blog, 14 November 2015.
During our continuous monitoring for a 24-hour period from November 11, 2015 to November 12, 2015, eight days after the initial discovery, the Chuxiong Archives website consistently presented malicious content injected by an attacker depending on the source IP and user agent. We believe that if a user were to visit the compromised website a second time following the initial exposure to the malicious code, the site would recognize the source IP and user-agent and simply remain dormant, not exhibiting any malicious behavior. Because of this anti-analysis/evasion technique, it may easily cause the belief that a website no longer poses a threat, when it remains infected.
At the time of this report, using our malicious web content scanning system, we have already discovered more than four thousands additional, similarly compromised websites globally exhibiting the same ability of being able to be dormant or active depending on source IP and user agent. Investigations regarding this campaign on a larger scale are ongoing and a second report detailing the similarly compromised websites will be published in the near future.