Swarming Against Citrix 0-Day Exploitation

GreyNoise observes adversary activity through our Global Observation Grid (GOG), a network of sensors that draws attacker scanning and exploitation onto infrastructure we control. This lets us study adversary infrastructure, tooling, and tradecraft directly, without waiting for a victim investigation. GreyNoise also expands the GOG through Project Swarm, which enables the broader security community to join the effort. The activity discussed in this blog was derived from a Swarm participant sensor. 

On 24 September 2026, a malicious cyber actor (MCA) used 149.104.78.141 to attempt zero-day exploitation against a Citrix NetScaler Gateway. At the time, there were no CVE-specific detections for the attack due to it occurring pre-disclosure. However, GreyNoise still detected and labeled the activity as fundamentally malicious within seconds due to behavioral detections. GreyNoise will not publish full details of the exploitation chain at this time. Patches are available and…