CVE-2023-27566: Live2D Cubism Editor Buffer Overflow

CVE-2023-27566 Overview

CVE-2023-27566 is an out-of-bounds write vulnerability in Cubism Core, a component of Live2D Cubism Editor version 4.2.03. The vulnerability allows attackers to trigger memory corruption through a specially crafted MOC3 file containing malicious Section Offset Table or Count Info Table data. When a user opens the malicious file, the application writes data beyond the intended memory boundaries, potentially leading to arbitrary code execution.

Critical Impact

This vulnerability enables attackers to execute arbitrary code with the privileges of the user running Live2D Cubism Editor by tricking them into opening a malicious MOC3 file.

Affected Products

• Live2D Cubism Editor version 4.2.03
• Applications using Cubism Core SDK with vulnerable MOC3 parsing logic
• Third-party applications that integrate Live2D Cubism SDK for model rendering

Discovery Timeline

• 2023-03-03 - CVE-2023-27566 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2023-27566

Vulnerability Analysis

The vulnerability exists in the Cubism Core component's handling of MOC3 file format parsing. MOC3 files are Live2D's proprietary model format containing structured data including Section Offset Tables and Count Info Tables that define memory layouts and data boundaries for model rendering.

When processing these tables, the Cubism Core parser fails to properly validate offset and count values before using them for memory operations. An attacker can craft a malicious MOC3 file with manipulated table entries that cause the application to write data outside the bounds of allocated memory buffers.

The attack requires local access and user interaction, as the victim must open the malicious MOC3 file in Live2D Cubism Editor. However, MOC3 files are commonly shared among digital artists and VTuber content creators, making social engineering attacks feasible within these communities.

Root Cause

The root cause is insufficient bounds checking when parsing Section Offset Table and Count Info Table structures within MOC3 files. The parser trusts offset and size values from the file without validating them against actual buffer sizes, leading to CWE-787 (Out-of-bounds Write). This allows attacker-controlled data to overwrite adjacent memory regions.

Attack Vector

The attack requires local file access and user interaction to open the malicious MOC3 file. An attacker could distribute crafted MOC3 files through community sharing platforms, asset marketplaces, or targeted phishing campaigns aimed at Live2D content creators. Once opened, the corrupted memory can be leveraged to hijack program execution flow.

The exploitation mechanism involves:

1. Creating a MOC3 file with malformed Section Offset Table entries pointing beyond allocated buffers
2. Distributing the file through channels where Live2D users acquire model assets
3. When the victim opens the file, the parser writes attacker-controlled data to out-of-bounds memory locations
4. The memory corruption can be leveraged to achieve arbitrary code execution

Detection Methods for CVE-2023-27566

Indicators of Compromise

• Unusual crash logs or exceptions in Live2D Cubism Editor related to memory access violations
• MOC3 files with abnormally large or negative offset values in Section Offset Table structures
• Unexpected child processes spawned by Live2D Cubism Editor application
• Memory access violation events in system logs originating from Cubism Editor processes

Detection Strategies

• Implement file integrity monitoring for MOC3 files in shared asset directories
• Deploy endpoint detection rules that monitor for memory corruption patterns in Live2D processes
• Use application whitelisting to prevent unexpected code execution from content creation tools
• Configure sandbox environments for opening untrusted MOC3 files from external sources

Monitoring Recommendations

• Monitor process behavior for Live2D Cubism Editor, alerting on unusual system calls or child process creation
• Implement network monitoring for unusual outbound connections from content creation applications
• Review file access patterns for MOC3 files originating from untrusted sources
• Configure crash dump analysis to identify exploitation attempts through memory corruption signatures

How to Mitigate CVE-2023-27566

Immediate Actions Required

• Update Live2D Cubism Editor to the latest version that addresses this vulnerability
• Avoid opening MOC3 files from untrusted or unknown sources
• Implement application sandboxing for content creation tools handling external assets
• Deploy endpoint protection solutions capable of detecting memory corruption exploitation attempts

Patch Information

Live2D has released updates to address this vulnerability. Users should update to the latest version of Cubism Editor as documented in the Live2D Cubism Update Notes. The patch includes improved validation of Section Offset Table and Count Info Table entries to prevent out-of-bounds memory writes.

Additional technical analysis of the vulnerability is available through the GitHub moc3ingbird Project and detailed security research documented in the Security Analysis on Live2D.

Workarounds

• Open untrusted MOC3 files only in isolated virtual machine environments
• Use file scanning tools to inspect MOC3 files for anomalous offset values before opening
• Disable automatic file association for MOC3 files to prevent accidental execution
• Restrict Live2D Cubism Editor network access to limit post-exploitation capabilities

# Example: Restrict network access for Live2D Cubism Editor on Windows using firewall
netsh advfirewall firewall add rule name="Block Live2D Outbound" dir=out program="C:\Program Files\Live2D Cubism\CubismEditor.exe" action=block

# Example: Run Live2D in a restricted environment on Linux
firejail --net=none --private live2d-cubism-editor