CVE-2020-27798 in UPX
Summary
by MITRE • 08/26/2022
An invalid memory address reference was discovered in the adjABS 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-2020-27798 represents a critical memory safety issue within the UPX (Ultimate Packer for eXecutables) 4.0.0 compression utility. This flaw manifests specifically within the adjABS function located in the p_lx_elf.cpp source file, demonstrating a classic invalid memory address reference that can lead to unpredictable system behavior and potential exploitation. The vulnerability is triggered when the software processes a specially crafted Mach-O file, which is a binary format commonly used on macOS and iOS operating systems. The issue arises from inadequate input validation and memory management within the decompression routine that handles Mach-O file structures, creating a scenario where the adjABS function attempts to access memory locations that are either unmapped or unauthorized for the current execution context.
The technical exploitation of this vulnerability follows a path that aligns with CWE-476, which describes NULL pointer dereferences, and CWE-125, which addresses out-of-bounds read conditions. When a malicious actor submits a crafted Mach-O file to UPX 4.0.0, the adjABS function processes the file's relocation entries without proper bounds checking. The function fails to validate the memory addresses referenced in the Mach-O file's relocation information, leading to a situation where the program attempts to access invalid memory locations. This condition can result in memory corruption, program crashes, or potentially more severe consequences depending on the execution environment and memory layout. The vulnerability operates within the context of the ATT&CK technique T1059.007, which involves execution through scripting languages, as the compromised software could be leveraged to execute arbitrary code through memory corruption attacks.
The operational impact of this vulnerability extends beyond simple software instability, as it represents a potential entry point for more sophisticated attacks within software supply chain security contexts. When UPX is used to compress legitimate executables, an attacker who can influence the compression process or gain access to the compressed binaries could exploit this weakness to compromise systems. The vulnerability affects systems running UPX 4.0.0 across various operating systems where the utility is deployed, including macOS, Linux, and Windows environments where UPX might be used for executable compression. The exploitation scenario typically involves a user or system administrator running UPX on a maliciously crafted Mach-O file, which could occur during software development, distribution, or even during routine system maintenance operations. This creates a significant risk for organizations that rely on UPX for executable compression, as the vulnerability could be leveraged to bypass security controls or gain unauthorized access to systems.
Mitigation strategies for CVE-2020-27798 should prioritize immediate patching of UPX 4.0.0 installations, as this vulnerability has been addressed in subsequent releases of the software. Organizations should implement strict file validation procedures before processing any executables through UPX, including signature verification and sandboxed analysis of suspicious files. The remediation process should also include monitoring for unauthorized UPX installations or modifications to existing installations, as attackers might attempt to deploy modified versions of the software to exploit this vulnerability. Security teams should consider implementing network-based detection measures that can identify attempts to process suspicious Mach-O files through UPX, as well as regular security assessments to ensure that all instances of UPX within the organization are properly updated and maintained. Additionally, the vulnerability serves as a reminder of the importance of proper memory management in security-critical software components and highlights the need for comprehensive input validation and bounds checking in all binary processing utilities.