CVE-2025-8854: Bulletphysics Pybullet Buffer Overflow

CVE-2025-8854 Overview

CVE-2025-8854 is a stack-based buffer overflow vulnerability affecting the LoadOFF function in bulletphysics bullet3 versions before 3.26. The vulnerability exists across all platforms and allows remote attackers to execute arbitrary code via a specially crafted OFF file containing an overlong initial token. This malicious file can be processed by the VHACD test utility or invoked indirectly through PyBullet's vhacd function.

Critical Impact

Successful exploitation enables remote code execution through malicious OFF files, potentially allowing attackers to gain complete control of affected systems running vulnerable versions of bullet3 or PyBullet.

Affected Products

• bulletphysics pybullet (versions before 3.26)
• bulletphysics bullet3 (versions before 3.26)
• Applications utilizing PyBullet's vhacd function for mesh decomposition

Discovery Timeline

• 2025-08-11 - CVE-2025-8854 published to NVD
• 2025-12-08 - Last updated in NVD database

Technical Details for CVE-2025-8854

Vulnerability Analysis

This vulnerability falls under CWE-120 (Buffer Copy without Checking Size of Input) and CWE-787 (Out-of-bounds Write). The flaw resides in the LoadOFF function within the VHACD component of the bullet3 physics engine. When parsing OFF (Object File Format) files, the function fails to properly validate the length of the initial token before copying it to a fixed-size stack buffer.

The vulnerability is triggered when a user opens or processes a maliciously crafted OFF file. Since this is a local attack vector requiring user interaction, the attacker must convince the victim to process the malicious file through the VHACD test utility or via PyBullet's vhacd function. Upon successful exploitation, the attacker can achieve arbitrary code execution with the privileges of the running process.

Root Cause

The root cause stems from improper bounds checking in the LoadOFF function located in main_vhacd.cpp. When the function reads the initial token from an OFF file, it copies the input data into a stack-allocated buffer without verifying that the input length does not exceed the buffer's capacity. This classic buffer overflow pattern allows an attacker to overwrite adjacent stack memory, including return addresses and saved registers.

Attack Vector

The attack requires a local attack vector with user interaction. An attacker must craft a malicious OFF file containing an excessively long initial token that exceeds the expected buffer size. The attack chain typically involves:

1. The attacker creates a malicious OFF file with an overlong initial token designed to overflow the stack buffer
2. The victim processes the file using the VHACD test utility directly or through PyBullet's vhacd function
3. The LoadOFF function copies the oversized token into the fixed stack buffer, overwriting critical stack data
4. The attacker's payload gains execution control when the corrupted return address is used

The vulnerability is documented in GitHub Bullet Physics Issue #4732, with the affected code located at main_vhacd.cpp line 472.

Detection Methods for CVE-2025-8854

Indicators of Compromise

• Presence of unusually large or malformed OFF files in application directories or temporary folders
• Crash dumps or core files from VHACD utilities or PyBullet processes indicating stack corruption
• Unexpected process behavior or child process spawning from bullet3-related applications
• Memory access violations or segmentation faults in applications processing 3D mesh files

Detection Strategies

• Monitor for abnormal process terminations in applications utilizing bullet3 or PyBullet libraries
• Implement file integrity monitoring on systems processing OFF files from untrusted sources
• Deploy endpoint detection rules for stack-based buffer overflow exploitation patterns
• Enable crash monitoring and analysis for physics simulation applications

Monitoring Recommendations

• Configure application crash reporting to capture and analyze stack traces from bullet3-related processes
• Implement input validation logging for applications that process OFF files
• Monitor system calls and memory operations in environments running PyBullet simulations
• Set up alerts for unusual file processing activities involving 3D mesh formats

How to Mitigate CVE-2025-8854

Immediate Actions Required

• Upgrade bulletphysics bullet3 to version 3.26 or later immediately
• Restrict processing of OFF files from untrusted or unknown sources
• Implement strict input validation for all 3D mesh file formats before processing
• Consider sandboxing applications that utilize VHACD or PyBullet functionality

Patch Information

The vulnerability is addressed in bulletphysics bullet3 version 3.26 and later. Organizations using affected versions should upgrade to the patched release. For applications using PyBullet, ensure the underlying bullet3 library is updated to version 3.26 or newer. Technical details and the fix can be reviewed in GitHub Bullet Physics Issue #4732.

Workarounds

• Avoid processing OFF files from untrusted sources until patching is complete
• Implement file size and content validation before passing OFF files to the LoadOFF function
• Run VHACD utilities and PyBullet applications with reduced privileges
• Use application sandboxing or containerization to limit the impact of potential exploitation

# Update bullet3/PyBullet to patched version
pip install --upgrade pybullet

# Verify installed version is 3.26 or later
python -c "import pybullet; print(pybullet.getAPIVersion())"