Discovering Effluence, a unique web shell accessible on every page of an infected Confluence

Earlier this year, we started hunting for possible new DeftTorero (aka Lebanese Cedar, Volatile Cedar) artifacts. This threat actor is believed to originate from the Middle East and was publicly disclosed to the cybersecurity community as early as 2015. Notably, no other intelligence was shared until 2021, which led us to speculate on a possible shift by the threat actor to more fileless/LOLBINS techniques, and the use of known/common offensive tools publicly available on the internet that allows them to blend in.

At the start of 2022, CrowdStrike Intelligence and CrowdStrike Services investigated an incident in which PROPHET SPIDER exploited CVE-2021-22941 — a remote code execution (RCE) vulnerability impacting Citrix ShareFile Storage Zones Controller — to compromise a Microsoft Internet Information Services (IIS) web server. The adversary exploited the vulnerability to deploy a webshell that enabled the downloading of additional tools. This incident highlights how PROPHET SPIDER continues to evolve their tradecraft while continuing to exploit known web-server vulnerabilities.