CVE-2020-27800 in UPX
Summary
by MITRE • 08/26/2022
A heap-based buffer over-read was discovered in the get_le32 function in bele.h in UPX 4.0.0 via a crafted Mach-O file.
Be aware that VulDB is the high quality source for vulnerability data.
Analysis
by VulDB Data Team • 04/11/2025
The vulnerability CVE-2020-27800 represents a critical heap-based buffer over-read flaw in the UPX 4.0.0 compression utility specifically within the get_le32 function located in the bele.h header file. This issue manifests when processing crafted Mach-O binary files, which are commonly used on macOS and iOS operating systems. The vulnerability stems from insufficient input validation and boundary checking within the decompression routines that handle little-endian 32-bit integer extraction from memory buffers. When an attacker provides a maliciously constructed Mach-O file, the get_le32 function attempts to read beyond the allocated heap memory boundaries, potentially exposing sensitive data or enabling arbitrary code execution.
The technical implementation of this vulnerability involves the improper handling of binary data structures during the decompression process of compressed executables. The bele.h file contains utility functions for byte order conversion and data extraction, with get_le32 specifically designed to extract 32-bit little-endian integers from memory locations. However, the function lacks proper bounds checking mechanisms that would prevent reading past the intended buffer limits. This flaw falls under CWE-125, which describes out-of-bounds read conditions, and represents a classic example of improper input validation in binary parsing routines. The vulnerability is particularly concerning because Mach-O files contain complex metadata structures where attackers can manipulate header fields to trigger the buffer over-read condition.
Operational impact assessment reveals significant security implications for systems running UPX 4.0.0, particularly in environments where executable files are frequently compressed and decompressed. Attackers could exploit this vulnerability through various attack vectors including malicious software distribution, supply chain attacks, or social engineering campaigns targeting developers who use UPX for executable compression. The vulnerability enables potential information disclosure where adjacent memory contents are read and potentially exposed to unauthorized parties. Additionally, the over-read condition may lead to application crashes or in more sophisticated attack scenarios, could facilitate privilege escalation or remote code execution depending on how the decompression process integrates with other system components. This vulnerability aligns with ATT&CK technique T1059.007 for execution through Mach-O files and represents a critical weakness in software supply chain security.
Mitigation strategies for CVE-2020-27800 require immediate action to upgrade to patched versions of UPX 4.0.1 or later, as the vulnerability has been addressed through proper bounds checking implementation in the affected functions. Organizations should implement comprehensive software inventory management to identify all systems running vulnerable UPX versions and ensure timely patch deployment across all environments. Network security controls including file integrity monitoring and suspicious file detection should be enhanced to identify potential exploitation attempts involving crafted Mach-O files. Security teams should also consider implementing sandboxing mechanisms for decompression operations and establish strict access controls for systems handling executable files. The vulnerability demonstrates the importance of rigorous input validation in binary parsing libraries and highlights the need for security-focused code reviews and static analysis tools to identify similar issues in other software components. System administrators should monitor for any signs of exploitation attempts and maintain detailed logging of decompression activities to support forensic analysis if incidents occur.