CVE-2023-34296

Executive Summary

CVE-2023-34296 is a critical out-of-bounds write vulnerability in Sante DICOM Viewer Pro, a medical imaging application used for viewing DICOM files. The flaw exists in the parsing of DCM files, where insufficient validation of user-supplied data can lead to a write past the end of an allocated object. An attacker can exploit this by convincing a user to open a malicious DCM file or visit a malicious page, resulting in remote code execution in the context of the current process. With a CVSS score of 7.8, this vulnerability poses a significant risk to healthcare environments where DICOM viewers are commonly deployed. No public exploit or patch is currently available, making detection and mitigation critical.

CVSS Breakdown & Threat Level

• CVSS Score: 7.8 (High)
• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
• Attack Vector: Network (AV:N) – Exploitable remotely.
• Attack Complexity: Low (AC:L) – No special conditions required.
• Privileges Required: None (PR:N) – No authentication needed.
• User Interaction: Required (UI:R) – Victim must open a malicious file or page.
• Scope: Unchanged (S:U) – Vulnerability does not affect other components.
• Confidentiality Impact: High (C:H) – Full data compromise possible.
• Integrity Impact: High (I:H) – Arbitrary code execution.
• Availability Impact: High (A:H) – Potential system crash or takeover.
• Threat Level: Critical – Exploitation could lead to full system compromise in medical environments.

Deep Dive & Mechanics

The vulnerability resides in the DCM file parsing routine of Sante DICOM Viewer Pro. DCM files are standard medical imaging files containing pixel data, metadata, and tags. The specific flaw is an out-of-bounds write (CWE-787) triggered when the parser processes a crafted DCM file. The lack of proper validation allows an attacker to supply data that causes the application to write beyond the allocated buffer, corrupting adjacent memory. This can be leveraged to overwrite function pointers or return addresses, leading to arbitrary code execution.

The attack vector is user interaction: the victim must open a malicious DCM file (e.g., via email, web download, or direct file access) or visit a malicious page that triggers the viewer to parse the file. Since DICOM viewers are often used in clinical settings, a successful exploit could allow an attacker to execute code with the privileges of the logged-in user, potentially accessing sensitive patient data or pivoting to other systems.

Vulnerable vs. Patched Code

No patched version is available. The vulnerable code likely involves a function that reads DICOM tags or pixel data without proper bounds checking. For example, a vulnerable snippet might look like:

void parse_dicom_tag(char *buffer, int length) {
    char tag_data[256];
    // No bounds check on length
    memcpy(tag_data, buffer, length); // Out-of-bounds write if length > 256
}

A patched version would include validation:

void parse_dicom_tag(char *buffer, int length) {
    char tag_data[256];
    if (length > sizeof(tag_data)) {
        // Handle error
        return;
    }
    memcpy(tag_data, buffer, length);
}

Since no patch exists, users must rely on mitigations.

Exploitation & Lab Setup

Red Team

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

Lab Setup:

• Attacker Machine: Kali Linux with Metasploit or custom exploit framework.
• Target Machine: Windows 10/11 with Sante DICOM Viewer Pro installed.
• Network: Both machines on the same LAN or attacker can deliver file via email/web.

Steps:

1. Craft Malicious DCM File: Use a fuzzer (e.g., AFL) or manual analysis to create a DCM file that triggers the out-of-bounds write. Overwrite a return address or function pointer with a shellcode address.
2. Deliver Payload: Host the file on a web server or send via email with social engineering (e.g., "Urgent patient scan").
3. Trigger Exploit: Victim opens the file in Sante DICOM Viewer Pro. The exploit executes shellcode, spawning a reverse shell or Meterpreter session.
4. Post-Exploitation: Escalate privileges, exfiltrate DICOM data, or pivot to internal systems.

Note: No public exploit code is available; this is a theoretical approach.

Blue Team

Objective: Detect and prevent exploitation of CVE-2023-34296.

Detection:

• Monitor for unusual DCM file downloads or email attachments.
• Use endpoint detection rules for out-of-bounds write behavior (e.g., via EDR alerts on memory corruption).
• Deploy network signatures for malicious DCM files (see Suricata rule below).

Prevention:

• Restrict execution of Sante DICOM Viewer Pro to authorized users only.
• Use application whitelisting to prevent untrusted binaries.
• Enable ASLR and DEP on Windows systems.
• Isolate DICOM viewers in a sandboxed environment (e.g., via AppLocker or Windows Sandbox).

Indicators of Compromise (IOCs)

• File Hashes: (No known samples; monitor for suspicious DCM files)
• Network Indicators: Outbound connections from Sante DICOM Viewer Pro to unknown IPs (e.g., for reverse shell).
• Process Behavior: Sante DICOM Viewer Pro crashing or exhibiting memory corruption (e.g., access violation errors).
• Registry/File System: Unusual files written to %TEMP% or %APPDATA% by the viewer process.
• YARA Rule: See below for detection of malicious DCM files.

Detection Engineering

YARA Rule

rule CVE_2023_34296_Malicious_DCM {
    meta:
        description = "Detects malicious DCM files exploiting CVE-2023-34296"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2023-34296"
    strings:
        $dcm_header = { 44 49 43 4D } // "DICM" magic bytes
        $large_tag = /[\x00-\xFF]{4}\x00\x00\x00\xFF/ // Potential oversized tag
    condition:
        $dcm_header at 128 and #large_tag > 0
}

Sigma Rule

title: Sante DICOM Viewer Pro Out-of-Bounds Write Exploit
id: 8a9b3c4d-5e6f-7a8b-9c0d-1e2f3a4b5c6d
status: experimental
description: Detects potential exploitation of CVE-2023-34296 via process crashes or memory corruption
author: Valters IT
date: 2025-04-10
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        Image|endswith: 'DicomViewerPro.exe'
        CommandLine|contains: '.dcm'
    condition: selection
falsepositives:
    - Legitimate DICOM file opening
level: high

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2023-34296 Sante DICOM Viewer Pro Out-of-Bounds Write Exploit"; flow:to_server,established; content:"|44 49 43 4D|"; offset:128; depth:4; content:"|FF|"; within:100; classtype:attempted-user; sid:1000001; rev:1;)

Remediation & Mitigation

• Patch Status: No official patch available. Contact Sante for updates.
• Mitigation:
  • Disable or restrict use of Sante DICOM Viewer Pro until a patch is released.
  • Use alternative DICOM viewers with active security support.
  • Implement strict file upload filters to block DCM files from untrusted sources.
  • Enable Windows Defender Exploit Guard (e.g., Controlled Folder Access) to protect sensitive directories.
  • Train users to avoid opening unsolicited DICOM files.
• Workaround: If the viewer must be used, run it in a sandboxed environment with minimal privileges.

Valters IT
Securing Digital Frontiers