Valkyrie Stealer: Anatomy of a Modern Infostealer

In today's cyber threat ecosystem, infostealers remain one of the most pervasive and destructive categories of malware, quietly siphoning credentials, session tokens, cryptocurrency wallets, messaging app tokens, and system artifacts while evading detection. Among these, Valkyrie Stealer malware has emerged as a significant modern threat, blending stealth, modular architecture, and advanced evasion mechanisms that challenge both desktop users and enterprise defenders. In this post, we'll dissect Valkyrie's technical workings, illustrate a full attack workflow, and provide actionable detection and defense strategies that both technical and non-technical readers can leverage.

At its core, Valkyrie Stealer malware is a Windows targeted infostealer written in C++, designed to harvest a broad range of sensitive user data and exfiltrate it to attacker controlled infrastructure. It is a malware as a service (MaaS) offering, meaning threat actors can purchase or subscribe to use it against their targets. Its design emphasizes stealth, anti-analysis measures, making it a highly effective threat seen increasingly in 2025.

Valkyrie Infostealer

Core Capabilities: What Valkyrie Steals & How

1. System Recon & Profiling

   1. Upon execution, Valkyrie conducts environment reconnaissance such as system and hardware info, OS version, n/w metadata etc. to tailor its behavior, gather context, and determine the best theft strategy

   2. This data is included in the final exfiltrated report to provide attackers with context about the environment.

2. Anti Analysis & Evasion Techniques

   1. Valkyrie checks for:

      1. Virtual machines, sandboxes, and analysis tools

      2. Watchdog timers

      3. Themida protection etc.

3. Credential & Browser Data Theft

   1. The stealer targets Chromium-based browsers (like Chrome, Edge, Brave) to extract passwords, cookies, autofill data etc.

   2. This is achieved by locating browser installation paths via registry entries, extracting the AES master key, parsing SQLite-based profile databases for credentials and other techniques

   3. Session tokens are extracted from known storage paths. Tokens are then validated via API calls to confirm user identities and additional metadata before exfiltration.

   4. Valkyrie looks for local wallet files and also steals game launcher tokens and configuration files

4. Screenshots & Process Enumeration

   1. To give attackers a real-time snapshot, the malware captures full screen images using GDI calls and enumerates running processes, which aids in contextual threat exploitation planning.

5. Data Packaging & Exfiltration

   1. After collection, Data is zipped into Valkyrie.zip.

   2. Encryption is applied using AES-GCM with hardcoded 32-byte keys and a random IV before transmission.

   3. Exfiltration occurs via HTTP POST to /api/log on attacker servers, often as a primary domain derived from a Steam profile with fallback infrastructure.

Blue Team Detection

Infostealers like Valkyrie often blend into legitimate traffic, so defenders must use behavioral indicators to identify suspicious activity

Indicators of Compromise (IOCs):

• Unknown outbound connections to domains like lylred.space or thenewflights.xyz on /api/log endpoints.

• Presence of Valkyrie.zip in Temp directories.

• Steam profile lookup behavior via HTTP GET to Steam community followed by unexpected C2 resolution.

Prevention & Hardening

• Block known malicious attachments and enforce attachment sandboxing.

• Enforce least privilege for local accounts and enable multi-factor authentication everywhere.

• Whitelist outbound destinations and inspect HTTP traffic for suspicious exfil patterns.

In the constantly evolving arms race between attackers and defenders, Valkyrie Stealer malware illustrates how modern infostealers combine stealth, versatility, and robust exfiltration mechanisms to threaten users and organizations alike. Understanding how it operates from anti-analysis evasion to credential exfiltration is essential for building resilient defenses. By combining behavioral detection, proactive prevention hardening, and continuous monitoring, defenders can significantly reduce exposure to these increasingly sophisticated threats.

Happy cyber-exploration! 🚀🔒

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-AJ