Attributed metadata history

STOCKSTAY Another Day: The Latest Addition to Turla’s Intelligence Gathering Apparatus

Written by: Jordan Jones Introduction  Google Threat Intelligence Group (GTIG) has conducted an in-depth analysis of a .NET backdoor, tracked as STOCKSTAY, that has been continually developed and deployed by the Russia-linked threat actor Turla (aka SUMMIT, Secret Blizzard, VENOMOUS BEAR, UAC-0194) since at least December 2022. Turla has deployed STOCKSTAY against government and military organizations in Ukraine, as well as entities with an interest in Italian foreign policy. Used for ongoing cyber espionage, this backdoor shares significant code and functional overlaps with KAZUAR, a successful toolkit previously attributed to Turla. The group has a long history of targeting a wide range of industries, with a particular focus on western Ministries of Foreign Affairs, and defense organizations within the context of heightened political tensions.  Turla, and specifically their longstanding Snake implant, has been publicly attributed by the United States Cybersecurity and Infrastructure Security Agency (CISA) to Center 16 of Russia’s Federal Security Service (FSB). Turla is one of the oldest known cyber espionage groups with suspected activity dating back to at least 2004. The actor remains active and continues to evolve its delivery methods, as demonstrated by its deployment of specialized scripts to intercept secure communications from Signal Messenger users, its hijacking of legacy criminal botnets to target Ukrainian organizations, and its recent campaigns targeting military defense sectors using the highly sophisticated KAZUAR toolkit. As part of our continued tracking of this group, this blog post provides an overview of our STOCKSTAY analysis, includes a timeline of key developmental and operational observations, and examines its similarities to KAZUAR to contextualize this new capability within Turla’s ever-growing arsenal. STOCKSTAY Overview STOCKSTAY is a multi-component backdoor written in .NET, using the Windows Forms framework, which communicates with its command and control (C2) via a secure WebSocket connection, utilizing the open-source websocket-sharp library. STOCKSTAY consists of several distinct components that communicate with one another via an inter-process communication (IPC) channel, based on the exchange of WM_COPYDATA messages.  STOCKSTAY was originally designed to masquerade as a stock market data viewing tool, incorporating this disguise in both its file naming scheme and its storage of implant configuration, control messages, and response data. While initial versions of the malware observed by GTIG retained the internal aspects of this disguise, in 2025 we identified variants of STOCKSTAY masquerading as other benign applications, such as PDF viewers and calculator utilities. Figure 1: Overview of STOCKSTAY malware architecture STOCKSTAY.STOCKBROKER STOCKSTAY.STOCKBROKER is a proxy-aware tunneler which provides network communication capabilities to the wider STOCKSTAY ecosystem. STOCKSTAY.STOCKBROKER, internally referred to as "net", can be instructed to establish a secure WebSocket connection to a specified remote server, after which it acts as a relay between the server and the STOCKSTAY.STOCKMARKET orchestrator. As a result, all C2 communication between STOCKSTAY and the configured C2 server are handled by STOCKSTAY.STOCKBROKER, isolating the malware’s network communications from other malicious host-based activity on the infected machine.  STOCKSTAY.STOCKMARKET STOCKSTAY.STOCKMARKET, internally referred to as “cor”, is the orchestrator of the STOCKSTAY ecosystem, and enables the implant’s configurability. The malware’s configuration is loaded from an encrypted on-disk configuration file which specifies several options regarding the malware’s execution, including the details of the remote WebSocket server required by STOCKSTAY.STOCKBROKER. The c

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