CVE-2024-9727

Executive Summary

CVE-2024-9727 is a critical use-after-free vulnerability in Trimble SketchUp Viewer, a widely used 3D modeling application. The flaw resides in the parsing of SKP files, where the software fails to validate the existence of an object before performing operations on it. This allows an attacker to craft a malicious SKP file that, when opened by a user, triggers a use-after-free condition, leading to remote code execution in the context of the current process. The vulnerability requires user interaction (opening a malicious file or visiting a malicious page) and has a CVSS score of 7.8 (High). No public exploit or patch is currently available, but the risk is significant due to the widespread use of SketchUp in architecture, engineering, and construction industries.

Supply Chain & Package Security

This vulnerability is not related to NPM, PyPI, Go, or Ruby packages. It affects a standalone desktop application (Trimble SketchUp Viewer) and is distributed via official channels. Supply chain risk is limited to the distribution of malicious SKP files through email, web downloads, or shared project files.

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: Local (requires user to open a malicious file)
• Attack Complexity: Low
• Privileges Required: None
• User Interaction: Required
• Scope: Unchanged
• Confidentiality Impact: High
• Integrity Impact: High
• Availability Impact: High

Threat Level: High. Although exploitation requires user interaction, the impact is complete compromise of the user's system. The vulnerability is in a widely used application, and the lack of a patch increases the risk.

Deep Dive & Mechanics

The vulnerability is a classic use-after-free (UAF) in the SKP file parser. SKP files are binary files containing 3D model data, including geometry, materials, and metadata. The parser reads these structures and allocates memory for objects. The flaw occurs when the parser frees an object but later attempts to access it without checking if it still exists. This can happen due to:

• Improper reference counting: The parser may decrement a reference count incorrectly, causing an object to be freed while still in use.
• Race conditions: In multi-threaded parsing, one thread may free an object while another thread accesses it.
• Malformed data: An attacker can craft an SKP file that causes the parser to free an object prematurely (e.g., by providing a dangling pointer or invalid index).

When the freed memory is reallocated by the attacker (e.g., via heap spraying), the parser's subsequent access to the original object can execute arbitrary code.

Root Cause: Lack of validation of object existence before use (CWE-416).

Vulnerable vs. Patched Code

Since no patch is available, we can only describe the vulnerable pattern:

Vulnerable Code (Hypothetical):

void ParseObject(Object* obj) {
    // ... parse data ...
    if (obj->type == TYPE_COMPLEX) {
        // Process complex object
        ProcessComplex(obj->complexData);
    }
    // Free object
    FreeObject(obj);
}

void ProcessComplex(ComplexData* data) {
    // Use-after-free: obj was freed, but data pointer is still used
    data->value = 42; // Accessing freed memory
}

Patched Code (Hypothetical):

void ParseObject(Object* obj) {
    // ... parse data ...
    if (obj->type == TYPE_COMPLEX) {
        // Process complex object before freeing
        ProcessComplex(obj->complexData);
    }
    // Free object only after all uses
    FreeObject(obj);
}

The fix would involve ensuring that all references to an object are released before freeing it, or using smart pointers/reference counting to manage object lifetimes.

Exploitation & Lab Setup

Red Team

Prerequisites:

• Trimble SketchUp Viewer (any version)
• Ability to craft a malicious SKP file

Exploitation Steps:

1. Craft Malicious SKP File: Use a hex editor or custom tool to modify a valid SKP file. Introduce a dangling pointer or invalid reference that triggers a use-after-free. For example, create an object that references itself in a way that causes premature freeing.
2. Heap Spray: To control the freed memory, include a heap spray payload in the SKP file (e.g., large arrays of data that fill the heap with attacker-controlled content).
3. Deliver Payload: Send the malicious SKP file to the target via email, download link, or shared drive.
4. Trigger Exploit: When the target opens the file in SketchUp Viewer, the UAF is triggered, and the attacker's shellcode executes.

Example Payload (Shellcode):

; Windows x64 MessageBox shellcode
xor rcx, rcx
mov rdx, 0x4242424242424242 ; "Hello" string
mov r8, 0x4242424242424242 ; "World" string
xor r9, r9
mov rax, 0x4242424242424242 ; MessageBoxA address
call rax

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

Blue Team

Detection:

• Monitor for unusual SKP file downloads or email attachments.
• Use endpoint detection and response (EDR) to detect heap spray patterns (e.g., large allocations of similar data).
• Enable application whitelisting to block untrusted SKP files.

Mitigation:

• Disable automatic file previews in email clients.
• Use sandboxing to open SKP files in isolated environments.
• Apply strict file access controls.

Indicators of Compromise (IOCs)

• File Hashes: (None available, but monitor for SKP files with unusual sizes or structures)
• Network Indicators: Connections to unknown IPs after opening SKP files
• Process Behavior: SketchUp Viewer crashing or exhibiting abnormal memory access patterns
• Registry Keys: (None specific)
• YARA Rule: See Detection Engineering

Detection Engineering

YARA Rule

rule CVE_2024_9727_SKP_UAF {
    meta:
        description = "Detects malicious SKP files exploiting CVE-2024-9727"
        author = "Valters IT"
        date = "2025-04-10"
        hash = "unknown"
    strings:
        $suspicious_pattern = { 00 00 00 00 00 00 00 00 } // Example: null pointer pattern
        $heap_spray = { 41 41 41 41 41 41 41 41 } // Example: heap spray marker
    condition:
        $suspicious_pattern or $heap_spray
}

Sigma Rule

title: CVE-2024-9727 - Trimble SketchUp Viewer SKP File Use-After-Free
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects potential exploitation of CVE-2024-9727 via SKP file parsing
author: Valters IT
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        Image|endswith: 'SketchUp.exe'
        CommandLine|contains: '.skp'
    condition: selection
falsepositives:
    - Legitimate SKP file usage
level: high

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2024-9727 - SKP File Download"; flow:to_server,established; content:"|00 00 00 00|"; depth:4; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable SKP file parsing in Trimble SketchUp Viewer if possible, or use an alternative viewer.
2. Implement application whitelisting to block untrusted SKP files.
3. Educate users not to open SKP files from untrusted sources.

Long-term:

• Monitor Trimble's security advisories for a patch.
• Consider using a sandboxed environment for opening SKP files.
• Apply the principle of least privilege to user accounts.

Workarounds:

• Use file scanning tools to detect malicious SKP files.
• Enable Windows Defender Exploit Guard to mitigate heap spray attacks.

Valters IT
Securing Digital Frontiers