CVE-2023-52277

Executive Summary

CVE-2023-52277 is a heap-based buffer overflow vulnerability in Royal RoyalTSX, a remote desktop and connection management application. The flaw resides in the RAPortCheck.createNWConnection function during SecureGatewayHost object processing. An attacker can craft a malicious .RTSZ file containing an overly long hostname. When a victim opens this file and clicks "Test Connection", the application suffers a heap memory corruption, leading to a denial of service (application crash) and potentially arbitrary code execution. The vulnerability is unpatched in versions prior to 6.0.2.1, and no official CVSS vector has been assigned, though the impact is severe due to the potential for remote code execution.

CVSS Breakdown & Threat Level

While no official CVSS vector is provided, based on the vulnerability characteristics, a reasonable assessment is:

• Attack Vector (AV): Local (L) – Requires user to open a malicious file.
• Attack Complexity (AC): Low (L) – No special conditions.
• Privileges Required (PR): None (N) – No authentication needed.
• User Interaction (UI): Required (R) – Victim must click "Test Connection".
• Scope (S): Unchanged (U) – Vulnerability affects only the vulnerable component.
• Confidentiality (C): High (H) – Potential for arbitrary code execution.
• Integrity (I): High (H) – Potential for arbitrary code execution.
• Availability (A): High (H) – Denial of service is immediate.

Estimated CVSS Score: 7.8 (High)

Threat Level: High – Exploitation requires user interaction but can lead to full system compromise.

Deep Dive & Mechanics

The vulnerability is a classic heap-based buffer overflow (CWE-122). The RAPortCheck.createNWConnection function, when processing a SecureGatewayHost object from an .RTSZ file, copies the hostname into a fixed-size heap buffer without proper bounds checking. By providing an extremely long hostname string, an attacker can overflow the buffer, corrupting adjacent heap memory.

Technical Flow:

1. The victim receives a malicious .RTSZ file (e.g., via email, download).
2. RoyalTSX parses the file, extracting connection details including the SecureGatewayHost hostname.
3. When the user clicks "Test Connection", the application calls RAPortCheck.createNWConnection.
4. This function allocates a heap buffer for the hostname but does not validate its length.
5. A strcpy or similar unsafe copy operation writes the attacker-controlled long hostname into the buffer, overflowing into adjacent heap metadata or other objects.
6. This corruption causes a heap memory corruption, typically resulting in an immediate application crash (denial of service). With careful heap grooming, an attacker could achieve arbitrary code execution.

Vulnerable vs. Patched Code

Vulnerable Code (Conceptual):

void RAPortCheck::createNWConnection(const char* hostname) {
    char buffer[256];
    strcpy(buffer, hostname); // Unsafe: no length check
    // ... use buffer for connection
}

Patched Code (Conceptual):

void RAPortCheck::createNWConnection(const char* hostname) {
    char buffer[256];
    strncpy(buffer, hostname, sizeof(buffer) - 1); // Safe: bounded copy
    buffer[sizeof(buffer) - 1] = '\0';
    // ... use buffer for connection
}

The patch introduces bounds checking using strncpy or similar safe functions, preventing the overflow.

Exploitation & Lab Setup

Red Team

Objective: Demonstrate denial of service or potential code execution.

Lab Setup:

• Windows 10/11 VM with RoyalTSX version 6.0.0.0 (vulnerable).
• Python 3 installed on attacker machine.

Exploit Script (Python):

import struct

# Craft malicious RTSZ file
# RTSZ is a ZIP-based format; we create a minimal file with a long hostname
# This is a simplified example; actual RTSZ structure may vary.

malicious_hostname = "A" * 1000  # Overflow trigger

# Minimal RTSZ structure (simplified)
rtsz_data = b"RTSZ"  # Magic bytes
rtsz_data += struct.pack("<I", len(malicious_hostname))
rtsz_data += malicious_hostname.encode()

with open("malicious.rtsz", "wb") as f:
    f.write(rtsz_data)

print("Malicious RTSZ file created: malicious.rtsz")

Execution:

1. Transfer malicious.rtsz to the victim VM.
2. Open the file in RoyalTSX.
3. Click "Test Connection" on the imported connection.
4. Observe application crash (heap corruption).

Note: For actual code execution, heap spraying and ROP chain construction would be required, which is beyond this basic PoC.

Blue Team

Detection:

• Monitor for abnormal process crashes of RoyalTSX.exe.
• Use Sysmon to log process termination events (Event ID 5).
• Enable Application Crash Dumps for analysis.

Prevention:

• Block .RTSZ file attachments in email gateways.
• Use AppLocker or WDAC to restrict execution of untrusted files.
• Deploy EDR with behavioral detection for heap corruption patterns.

Indicators of Compromise (IOCs)

• File Hashes (SHA256): (Example – actual hash depends on crafted file)
  • malicious.rtsz: e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855
• Process: RoyalTSX.exe crashing with exception code 0xc0000374 (Heap Corruption).
• Registry: (None specific)
• Network: (None – local file exploitation)
• YARA Rule: See Detection Engineering.

Detection Engineering

YARA Rule

rule CVE_2023_52277_RoyalTSX_HeapOverflow {
    meta:
        description = "Detects malicious RTSZ files exploiting CVE-2023-52277"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2023-52277"
    strings:
        $magic = "RTSZ"
        $long_hostname = /[A-Za-z0-9._-]{500,}/  // Hostname > 500 chars
    condition:
        $magic at 0 and $long_hostname
}

Sigma Rule

title: RoyalTSX Heap Corruption via Malicious RTSZ File
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects RoyalTSX process crash due to heap corruption from CVE-2023-52277
author: Valters IT
logsource:
    product: windows
    service: application
detection:
    selection:
        EventID: 1000  # Application Error
        ApplicationName: 'RoyalTSX.exe'
        ExceptionCode: '0xc0000374'  # Heap Corruption
    condition: selection
falsepositives:
    - Legitimate crashes due to other bugs
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2023-52277 RoyalTSX RTSZ File Download"; flow:to_server; content:"|52 54 53 5a|"; distance:0; within:4; classtype:attempted-dos; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate:

1. Upgrade to RoyalTSX version 6.0.2.1 or later.
2. If upgrade is not possible, disable the "Test Connection" feature or restrict its use.
3. Educate users not to open .RTSZ files from untrusted sources.

Long-term:

• Implement input validation for all user-supplied data in connection files.
• Use safe string functions (e.g., strncpy, snprintf) throughout the codebase.
• Conduct regular security audits and fuzz testing.

Detection:

• Deploy YARA and Sigma rules to detect malicious RTSZ files and exploitation attempts.
• Monitor for abnormal crashes of RoyalTSX.exe.

Valters IT
DevSecOps & Cyber Threat Intelligence