Published: June 19, 2025
By: SOCDFIR

🔍 Summary

Google has patched CVE‑2025‑2783, a high-severity zero-day vulnerability affecting Google Chrome. The flaw enables an attacker to escape the Chrome sandbox, bypassing its core isolation model to execute malicious code directly on the host system.

This exploit was used by the suspected APT group “TaxOff” to deliver a stealthy loader and backdoor dubbed Trinper, targeting finance, government, and defense sectors via waterholing attacks.

⚙️ CVE Details

• CVE ID: CVE-2025-2783
• Severity: High
• CVSS v3.1 Score: 8.8
• Vector: AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H
• Patched Version: Chrome 125.0.6422.121 (Released June 17, 2025)

📖 Technical Breakdown

🧬 Vulnerability Class

This is a use-after-free (UAF) vulnerability in the V8 JavaScript engine. It involves improperly freed memory tied to ArrayBufferView objects, allowing attackers to gain arbitrary memory access.

📌 Exploitation Flow

1. Heap Spraying: JavaScript sprays the heap with predictable objects.
2. Trigger UAF: Engine-internal misuse of detachArrayBuffer leads to dangling pointers.
3. Memory Hijacking: Attacker overlaps reused memory with shellcode or function pointer corruption.
4. Sandbox Escape: IPC mechanisms in Chrome are used to break out into the browser process.
5. Payload Drop: The backdoor (Trinper) is delivered using rundll32.exe and persists via the registry.

🖥️ Trinper Payload Behavior

• Fileless persistence: Executes in memory, writes to registry HKCU\Software\Microsoft\Windows\CurrentVersion\Run
• C2 Communication: Encrypted HTTPS on port 4433 with custom headers
• Capabilities: File access, keylogging, lateral movement via WMI, screen capture

🧪 Proof of Concept Explained

🔧 Step-by-Step

1. Heap Spraying

let spray = [];
for (let i = 0; i < 10000; i++) {
  spray.push(new Uint8Array(1024 * 10));
}
  

This allocates a large number of predictable memory blocks to increase the chance that freed memory gets reallocated where the attacker wants it.2. Triggering Use-After-Free

let buffer = new ArrayBuffer(0x1000);
let view = new Uint8Array(buffer);

// Pseudo-vulnerable call simulating engine behavior
%DetachArrayBuffer(buffer); 
view[0] = 0x41;  // Accessing freed memory (dangling pointer)
  

While %DetachArrayBuffer is not available in production JS, this simulates how a bug in the V8 internals might allow access to freed memory. Attackers exploit such behavior to leak addresses or overwrite function pointers.3. ROP Chain or Shellcode

The attacker crafts fake object structures or uses JIT spraying to redirect execution, typically into VirtualProtect or other Windows API calls, chaining this with IPC abuse to break the sandbox.

💥 Why This Works

Chrome’s sandbox isolates the renderer process from the OS, but use-after-free bugs can manipulate memory in ways that defeat these controls. With a working exploit chain, attackers can execute native code outside the sandbox—granting full access to the system if the browser runs with user-level privileges.

🛡️ Detection & Mitigation

🔧 Mitigation Actions

• Update Chrome to 125.0.6422.121 or later on all endpoints.
• Use AppLocker or WDAC to block execution of DLLs from temp/user-writeable directories.
• Implement browser isolation for sensitive environments (e.g., containers or VMs).
• Use GPO to restrict unsafe Chrome flags (block --no-sandbox, disable remote debugging).

🔍 Threat Hunting Tips

• Search for Chrome spawning child processes like cmd.exe, powershell.exe, or rundll32.exe
• Hunt for suspicious new Run key entries in the Windows registry.
• Inspect outbound HTTPS traffic over odd ports (4433, 8443) with malformed headers.
• Scan endpoint memory for suspicious JavaScript or JIT artifacts in browser processes.

🔗 MITRE ATT&CK Mapping

• Initial Access: T1189 (Drive-by Compromise)
• Execution: T1059.003 (JavaScript)
• Defense Evasion: T1218 (Signed Binary Proxy Execution)
• Persistence: T1547.001 (Registry Run Keys)
• Command and Control: T1071.001 (Web Protocols)

📚 References

• Google Chrome Release Blog
• CISA KEV Catalog
• V8 JavaScript Engine Documentation
• MITRE ATT&CK Framework

🧠 Final Thoughts

This zero-day demonstrates the continued high value of JavaScript engine vulnerabilities to advanced attackers. Even with sandboxing, an unpatched browser is a doorway into the OS. SOC and DFIR teams must act rapidly—patch, monitor, and hunt behaviorally. If you’re not watching your endpoints’ browsers, someone else might be.