Deep Dive: How Vidar Infostealer Defeats Chrome’s Application-Bound Encryption

In a sophisticated evolution of credential theft, operators of the Vidar infostealer have developed a highly effective evasion technique designed to circumvent Google Chrome’s Application-Bound Encryption (ABE). Introduced in 2024, ABE was implemented as a robust defense mechanism to tie sensitive browser data—such as cookies and saved credentials—to the specific application instance that encrypted them.

Recent telemetry from Gen Threat Labs reveals that the latest Vidar iterations are being distributed via weekly updates. These updates employ a complex operational chain involving process forking, memory pattern scanning, and Asynchronous Procedure Call (APC) injection to extract the browser’s master decryption key directly from live memory.

The Challenge: Chrome’s ABE Architecture

The core objective for any modern infostealer is to acquire the browser’s v20_master_key. Without this key, the ABE-protected data remains inaccessible. On a physical disk, this key is protected by two layers of CryptProtectData. However, the real hurdle lies in how Chrome handles this key during runtime.

In a live environment, Chrome secures the key using CryptProtectMemory combined with the CRYPTPROTECTMEMORY_SAME_PROCESS flag. This specific flag creates a formidable barrier: the key cannot be extracted and decrypted offline by an external process. To successfully decrypt the material, an attacker must invoke the complementary CryptUnprotectMemory function from within the active, legitimate browser process context.

The Vidar Bypass: Exploiting Process Context

Rather than attempting the futile task of disk-based extraction, Vidar shifts its focus to the browser’s live memory space. When a Chrome instance is currently active, the malware obtains a handle to the process with specific read permissions and executes NtCreateProcessEx using a null section handle.

This maneuver creates a silent, threadless fork of the browser. This results in a “copy-on-write” memory snapshot—a frozen duplicate of the process that does not trigger active execution, effectively flying under the radar of many standard endpoint security tools.

If no Chrome instance is detected, Vidar proactively launches a hidden instance using the CreateDesktopA command. It creates a hidden desktop (formatted as v20_%d) and executes the browser with the flags --no-first-run --disable-gpu about:blank to minimize the footprint.

Memory Scanning and Pattern Matching

Once the forked process is established, Vidar begins an intensive enumeration of the virtual memory using NtQueryVirtualMemory. To accelerate the search, the malware deploys up to 64 parallel worker threads to scan all committed and readable memory regions for a specific 32-byte signature.

The malware is hunting for a specific sequence that decodes to the ASCII string v20\x00. This sequence identifies a specific node within Chromium’s internal Encryptor::KeyRing map structure. By locating this pointer, Vidar gains a direct path to the encrypted master key. To ensure accuracy and avoid zero-filled false positives, the malware utilizes a majority-voting scheme to validate candidate addresses.

The Final Extraction: APC Injection

After pinpointing the candidate address, Vidar must force the legitimate browser process to decrypt the data for it. It achieves this via Asynchronous Procedure Call (APC) injection, choosing between two methods based on the detected security posture of the host:

• The Classic Method: Used when high-end security solutions (like EDRs from ESET or Bitdefender) are detected. Vidar creates a suspended remote thread, queues the APC, and then resumes the thread to force execution.
• The Special Method: The default, stealthier approach. It locates an existing, active browser thread and queues a specialized user APC that executes immediately, bypassing the need for the thread to enter an “alertable wait state.”

As noted by researchers at Gendigital, the APC function decrypts the data in place. Vidar then utilizes a second process fork to read the newly decrypted key via NtReadVirtualMemory. To confirm success, it attempts an AES-256-GCM decryption of the ABE-protected data using BCryptDecrypt.

To maintain a low forensic profile, the malware is programmed to immediately inject a follow-up APC to re-encrypt the key in memory, effectively “cleaning up” its tracks and restoring the browser to its original state. If the decryption attempt fails, Vidar will terminate all active browser instances and relaunch them to attempt the cycle again.

Defensive Implications and Detection Strategies

This methodology is particularly dangerous because it avoids traditional, “noisy” code injection. Instead, it hijacks legitimate Windows APC mechanisms—processes that many endpoint detection and response (EDR) systems do not monitor with sufficient granularity.

Threat Hunters should focus on the following indicators:

• Suspicious NtCreateProcessEx calls characterized by null section handles.
• Unexpected or rapid APC queuing directed into legitimate browser process threads.
• Unusual process forking behavior involving Chrome/Chromium binaries.

Primary Indicator of Compromise (IoC):
Organizations should immediately scan for the following Vidar 2.1 SHA-256 hash:
459daa809751e73f60fbbe4384a7d1653c36bb06945e4eb3635270924241100a