CVE-2025-5481

Executive Summary

CVE-2025-5481 is a critical remote code execution vulnerability in Sante DICOM Viewer Pro, a medical imaging application used for viewing DICOM files. The flaw resides in the parsing of DCM files, where an out-of-bounds write occurs due to insufficient validation of user-supplied data. An attacker can exploit this by convincing a user to open a malicious DCM file or visit a crafted web page, leading to arbitrary 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, but the technical details from ZDI (ZDI-CAN-26168) indicate a high likelihood of weaponization.

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) – Exploit can be delivered 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) – Exploit affects only the vulnerable component.
• Confidentiality Impact: High (C:H) – Full data access possible.
• Integrity Impact: High (I:H) – Arbitrary code execution.
• Availability Impact: High (A:H) – Potential for denial of service or full compromise.

Threat Level: Critical for healthcare environments. The lack of a patch and the nature of DICOM file sharing in medical workflows increase the risk of targeted attacks.

Deep Dive & Mechanics

The vulnerability is a classic out-of-bounds write (CWE-787) in the DCM file parsing routine of Sante DICOM Viewer Pro. DICOM files contain structured metadata and pixel data, often with tags and sequences. The flaw occurs when the parser processes a specially crafted DCM file that includes an element with an incorrect length field or an oversized value, causing the parser to write data beyond the allocated buffer.

Technical Breakdown:

1. Trigger: The attacker crafts a DCM file with a manipulated tag (e.g., (7FE0,0010) Pixel Data) where the length field is set to a value larger than the actual allocated buffer.
2. Parsing: The viewer reads the DICOM dataset and attempts to copy the pixel data into a heap buffer. Without proper bounds checking, the copy operation writes past the end of the buffer.
3. Exploitation: The out-of-bounds write corrupts adjacent heap metadata or other objects, allowing the attacker to overwrite function pointers or return addresses. This leads to arbitrary code execution.

Root Cause: Lack of validation of the length field in DICOM elements, specifically during the parsing of pixel data or other large binary segments.

Vulnerable vs. Patched Code

Since no patch is available, the vulnerable code is presumed to be in the DCM parsing module (e.g., DcmFileParser.cpp or similar). A patched version would include bounds checking before memory copy operations.

Vulnerable Code (Conceptual):

void ParseDCMElement(char* buffer, uint32_t length) {
    char* data = new char[length];
    memcpy(data, buffer, length); // No check if length exceeds allocated size
}

Patched Code (Conceptual):

void ParseDCMElement(char* buffer, uint32_t length, uint32_t maxSize) {
    if (length > maxSize) {
        // Handle error or truncate
        length = maxSize;
    }
    char* data = new char[length];
    memcpy(data, buffer, length);
}

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• Sante DICOM Viewer Pro (any version)
• A crafted DCM file with a malicious pixel data tag

Steps:

1. Craft the DCM file: Use a hex editor or a script to modify a valid DCM file. Set the length field of the Pixel Data tag (7FE0,0010) to a value larger than the actual data (e.g., 0xFFFFFFFF).
2. Deliver the file: Host the file on a web server or send it via email. The victim must open it with Sante DICOM Viewer Pro.
3. Trigger the exploit: When the viewer parses the file, the out-of-bounds write occurs. If the attacker has placed shellcode in the heap, they can achieve code execution.

Example Payload (Conceptual):

# Craft a malicious DCM file
import struct

def create_malicious_dcm():
    # DICOM preamble and meta information
    dcm = b'\x00' * 128 + b'DICM'
    # Add a malicious Pixel Data element
    tag = struct.pack('<HH', 0x7FE0, 0x0010)  # Pixel Data tag
    length = struct.pack('<I', 0xFFFFFFFF)    # Oversized length
    data = b'A' * 100  # Small data, but length says huge
    dcm += tag + length + data
    return dcm

with open('malicious.dcm', 'wb') as f:
    f.write(create_malicious_dcm())

Blue Team (Detection & Defense)

Detection:

• Monitor for unusual DCM files with oversized length fields.
• Use network monitoring to detect DICOM file transfers from untrusted sources.
• Deploy endpoint detection rules for heap corruption or out-of-bounds writes.

Defense:

• Restrict execution of Sante DICOM Viewer Pro to trusted users only.
• Use application whitelisting to prevent unknown executables.
• Implement file integrity monitoring for DCM files.

Indicators of Compromise (IOCs)

• File Hashes: (Example – replace with actual if available)
  • malicious.dcm – SHA256: e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855
• Network Indicators:
  • Outbound connections from Sante DICOM Viewer Pro to unknown IPs (e.g., 192.168.1.100:4444)
• Process Indicators:
  • SanteDicomViewerPro.exe spawning cmd.exe or powershell.exe
• Registry/File System:
  • Creation of suspicious files in %TEMP% or %APPDATA%

Detection Engineering

YARA Rule

rule CVE_2025_5481_Sante_DICOM_OOBW {
    meta:
        description = "Detects malicious DCM files exploiting CVE-2025-5481"
        author = "Valters IT"
        date = "2025-04-01"
        reference = "ZDI-CAN-26168"
    strings:
        $dicom_magic = "DICM"
        $pixel_data_tag = { E0 7F 10 00 }  // Little-endian tag (7FE0,0010)
        $large_length = { FF FF FF FF }    // 0xFFFFFFFF length
    condition:
        $dicom_magic at 128 and $pixel_data_tag and $large_length
}

Sigma Rule

title: CVE-2025-5481 Sante DICOM Viewer Pro OOBW Exploit
id: 12345678-1234-1234-1234-123456789abc
status: experimental
description: Detects potential exploitation of CVE-2025-5481 via DCM file parsing
author: Valters IT
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        Image|endswith: '\SanteDicomViewerPro.exe'
        CommandLine|contains: 'malicious.dcm'
    condition: selection
falsepositives:
    - Legitimate DCM files with unusual lengths (rare)
level: high

Suricata Rule

alert tcp any any -> any any (msg:"CVE-2025-5481 Sante DICOM Viewer Pro OOBW Exploit"; flow:to_server,established; content:"DICM"; offset:128; depth:4; content:"|E0 7F 10 00|"; distance:0; within:4; content:"|FF FF FF FF|"; distance:0; within:4; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable or restrict Sante DICOM Viewer Pro until a patch is released.
2. Implement network segmentation to isolate DICOM viewers from the internet.
3. Use application control to block execution of untrusted DCM files.

Long-term Fix:

• Monitor vendor advisories for a patch. Apply as soon as available.
• Consider alternative DICOM viewers with active security support.

Workarounds:

• Enable ASLR and DEP on the system.
• Use a sandbox or virtual machine for viewing untrusted DCM files.

Valters IT – Securing Healthcare, One Byte at a Time.