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Since April 2024, the threat actor Marbled Dust has been exploiting a zero-day vulnerability (CVE-2025-27920) in the Output Messenger chat application, targeting user accounts that have not applied necessary fixes. This exploitation has resulted in the collection of sensitive data from users in Iraq, specifically linked to the Kurdish military. Microsoft has high confidence in this assessment and notes that Marbled Dust conducts reconnaissance to identify potential targets using Output Messenger. Marbled Dust has successfully utilized this vulnerability to deploy malicious files and exfiltrate data. Microsoft notified the application’s developer, Srimax, about the vulnerability, leading to the release of a software update. A second vulnerability (CVE-2025-27921) was also found, but no exploitation of this second flaw has been observed. The zero-day vulnerability allows an authenticated user to upload malicious files to the server's startup directory. Marbled Dust has exploited this flaw to place a backdoor file, OMServerService.vbs, in the startup folder, enabling them to access communications and sensitive data indiscriminately. The attack chain begins with Marbled Dust gaining access to the Output Messenger Server Manager, likely through DNS hijacking or other credential interception techniques. Once inside, they exploit the vulnerability to drop malicious files, including a GoLang backdoor, which connects to a Marbled Dust command-and-control domain for data exfiltration. To mitigate this threat, Microsoft recommends updating to the latest version of Output Messenger, activating various security protections, and implementing rigorous vulnerability management strategies. Microsoft Defender XDR customers can identify potential threat activity through specific alerts related to Marbled Dust and utilize advanced hunting queries for detection. Indicators of compromise include traffic to the domain api.wordinfos[.]com, associated with Marbled Dust activities.