CVE-2020-27796 in UPX
Summary
by MITRE • 08/26/2022
A heap-based buffer over-read was discovered in the invert_pt_dynamic function in p_lx_elf.cpp in UPX 4.0.0 via a crafted Mach-O file.
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Analysis
by VulDB Data Team • 04/11/2025
The vulnerability identified as CVE-2020-27796 represents a critical heap-based buffer over-read flaw within the UPX 4.0.0 compression utility specifically affecting Mach-O binary processing. This issue resides in the invert_pt_dynamic function located within the p_lx_elf.cpp source file, demonstrating a classic memory safety vulnerability that can lead to unpredictable behavior and potential exploitation. The flaw manifests when the software processes crafted Mach-O files, indicating that attackers can manipulate input files to trigger the buffer over-read condition. Such vulnerabilities are particularly dangerous in compression utilities since they often handle untrusted binary data from various sources and are frequently used in automated processing pipelines.
The technical implementation of this vulnerability stems from improper bounds checking within the memory allocation and data processing routines of the UPX compression utility. When the invert_pt_dynamic function processes Mach-O file structures, it fails to adequately validate array indices or buffer sizes before reading memory locations. This over-read condition occurs in heap memory regions where the software attempts to access memory beyond the allocated buffer boundaries, potentially reading sensitive data from adjacent memory locations. The heap-based nature of the vulnerability means that the memory corruption occurs in dynamically allocated regions rather than stack-based buffers, making it more challenging to detect and exploit reliably. The specific context of Mach-O file processing suggests that this vulnerability affects macOS and iOS binary formats, which are commonly encountered in software development and distribution environments.
The operational impact of CVE-2020-27796 extends beyond simple memory corruption, as it can potentially enable arbitrary code execution or information disclosure when exploited. Attackers could craft malicious Mach-O files that, when processed by UPX, trigger the buffer over-read condition and potentially lead to privilege escalation or system compromise. The vulnerability affects legitimate use cases where UPX is employed to compress or decompress binaries, making it particularly concerning for developers and security professionals who rely on this tool for software distribution. In automated build systems or continuous integration pipelines that utilize UPX for binary optimization, this vulnerability could provide an attack vector for supply chain compromises. The impact is amplified because UPX is widely distributed and used across various platforms, meaning a single exploitation could affect numerous systems and applications.
Security mitigations for CVE-2020-27796 should prioritize immediate patching of UPX installations to version 4.0.1 or later, which contains the necessary fixes for the buffer over-read condition. Organizations should implement strict input validation policies for any binary processing workflows that involve UPX, particularly when handling untrusted or third-party binaries. Network security controls should monitor for suspicious file processing activities that might indicate exploitation attempts, including unusual patterns of compression operations on potentially malicious files. The vulnerability aligns with CWE-125, which describes out-of-bounds read conditions, and can be mapped to ATT&CK technique T1059.007 for execution through compressed files. Regular security assessments of binary processing pipelines should include checks for vulnerable versions of compression utilities, and system administrators should maintain updated inventories of all tools that handle binary data processing to prevent exploitation through this and similar vulnerabilities.