CVE-2023-32133

Executive Summary

CVE-2023-32133 is a critical out-of-bounds write vulnerability in Sante DICOM Viewer Pro, specifically during the parsing of J2K (JPEG 2000) images. The flaw allows a remote attacker to execute arbitrary code on the affected system by tricking a user into opening a malicious J2K file or visiting a crafted web page. The vulnerability resides in the lack of proper bounds checking when processing crafted data within a J2K image, leading to a write past the end of an allocated buffer. With a CVSS score of 7.8, this vulnerability poses a significant risk to healthcare and medical imaging environments where DICOM viewers are commonly used. No public proof-of-concept or exploit code is currently available, and no official patch has been released by the vendor.

CVSS Breakdown & Threat Level

• CVSS Score: 7.8 (High)
• Attack Vector: Local (requires user interaction)
• Attack Complexity: Low
• Privileges Required: None
• User Interaction: Required
• Scope: Unchanged
• Confidentiality Impact: High
• Integrity Impact: High
• Availability Impact: High

The threat level is elevated due to the potential for remote code execution in the context of the current user, which could lead to full system compromise. The low attack complexity and lack of privileges required make this an attractive target for attackers, especially in targeted attacks against healthcare organizations.

Deep Dive & Mechanics

The vulnerability is triggered during the parsing of J2K images within Sante DICOM Viewer Pro. The application fails to validate the size of data written to a buffer when processing specially crafted J2K image data. An attacker can embed malicious data within a J2K file that, when parsed, causes a write operation to exceed the allocated buffer boundary. This out-of-bounds write can corrupt adjacent memory, potentially leading to arbitrary code execution.

The specific flaw is in the handling of J2K image components, where the application does not properly check the length of data before copying it into a fixed-size buffer. By manipulating the image dimensions, tile sizes, or other parameters, an attacker can cause the application to write beyond the buffer's limits. This is a classic buffer overflow vulnerability (CWE-787) that can be exploited to overwrite critical data structures or inject shellcode.

Vulnerable vs. Patched Code

Since no official patch is available, a direct code comparison is not possible. However, the vulnerable code likely resembles:

// Vulnerable pseudo-code
void parse_j2k_image(uint8_t *data, size_t size) {
    uint8_t buffer[1024];
    // No bounds check
    memcpy(buffer, data, size);
}

A patched version would include proper bounds checking:

// Patched pseudo-code
void parse_j2k_image(uint8_t *data, size_t size) {
    uint8_t buffer[1024];
    if (size > sizeof(buffer)) {
        // Handle error
        return;
    }
    memcpy(buffer, data, size);
}

Exploitation & Lab Setup

Red Team

Objective: Achieve remote code execution on a target running Sante DICOM Viewer Pro.

Lab Setup:

• Windows 10/11 VM with Sante DICOM Viewer Pro installed.
• Python 3.x for crafting malicious J2K files.
• Debugger (e.g., x64dbg) for analysis.

Steps:

1. Craft a malicious J2K file with oversized data in a specific field (e.g., image width or tile offset).
2. Host the file on a web server or send via email.
3. Convince the target user to open the file in Sante DICOM Viewer Pro.
4. The out-of-bounds write overwrites a return address or function pointer.
5. Redirect execution to shellcode embedded in the J2K file.

Example Python script to generate a malicious J2K file:

import struct

def create_malicious_j2k():
    # Craft a minimal J2K header with oversized data
    header = b'\x00\x00\x00\x0c'  # J2K signature
    header += b'\x6a\x50\x20\x20'  # JPEG 2000 signature
    header += b'\x0d\x0a\x87\x0a'  # File type box
    # Add malicious data to trigger overflow
    overflow_data = b'A' * 2048  # Exceeds buffer size
    return header + overflow_data

with open('malicious.j2k', 'wb') as f:
    f.write(create_malicious_j2k())

Blue Team

Detection:

• Monitor for unusual J2K files being opened by Sante DICOM Viewer Pro.
• Use process monitoring to detect abnormal memory writes or crashes.
• Implement application whitelisting to prevent execution of untrusted DICOM viewers.

Mitigation:

• Restrict user permissions to prevent exploitation in the context of a low-privileged user.
• Use endpoint detection and response (EDR) tools to detect exploitation attempts.
• Educate users about the risks of opening unsolicited DICOM files.

Indicators of Compromise (IOCs)

• File Hashes (SHA256): (Example, not actual)
  • e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855
• Network Indicators:
  • Connections to known malicious IPs hosting J2K files.
• Process Indicators:
  • Sante DICOM Viewer Pro crashing or exhibiting abnormal memory usage.
• Registry Keys:
  • HKLM\Software\Sante\DICOM Viewer Pro\* (modified after exploitation)

Detection Engineering

YARA Rule

rule CVE_2023_32133_J2K_Overflow {
    meta:
        description = "Detects malicious J2K files targeting CVE-2023-32133"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2023-32133"
    strings:
        $j2k_header = { 00 00 00 0C 6A 50 20 20 0D 0A 87 0A }
        $overflow = { 41 41 41 41 }  // 'AAAA' pattern
    condition:
        $j2k_header at 0 and #overflow > 100
}

Sigma Rule

title: CVE-2023-32133 Exploitation Attempt via J2K File
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects attempts to exploit CVE-2023-32133 by opening a malicious J2K file in Sante DICOM Viewer Pro
author: Valters IT
date: 2025-04-10
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        Image|endswith: 'DicomViewerPro.exe'
        CommandLine|contains: '.j2k'
    condition: selection
falsepositives:
    - Legitimate use of J2K files
level: high

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2023-32133 J2K File Download Attempt"; flow:to_server,established; content:"|00 00 00 0C 6A 50 20 20 0D 0A 87 0A|"; depth:12; classtype:attempted-user; sid:1000001; rev:1;)

Remediation & Mitigation

• Immediate: Disable or restrict the use of Sante DICOM Viewer Pro until a patch is available.
• Workaround: Use an alternative DICOM viewer that is not affected by this vulnerability.
• Long-term: Monitor the vendor's website for updates and apply patches as soon as they are released.
• Compensating Controls: Implement application control policies to block execution of untrusted DICOM files. Use network segmentation to limit exposure of medical imaging systems.

Valters IT
Securing Digital Frontiers