CVE-2020-27797 in UPX
Summary
by MITRE • 08/26/2022
An invalid memory address reference was discovered in the elf_lookup 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-2020-27797 represents a critical memory safety issue within the UPX (Ultimate Packer for eXecutables) 4.0.0 compression utility specifically affecting its handling of Mach-O binary formats. This flaw exists in the elf_lookup function located within the p_lx_elf.cpp source file, demonstrating a classic invalid memory address reference that can lead to arbitrary code execution or system instability. The vulnerability manifests when UPX processes maliciously crafted Mach-O files, exploiting improper memory management during the lookup process for ELF (Executable and Linkable Format) structures within these binary files.
The technical implementation of this vulnerability stems from inadequate input validation and memory boundary checking within the elf_lookup function. When UPX encounters a malformed Mach-O file, the function fails to properly validate memory addresses before dereferencing them, creating a scenario where attackers can manipulate the execution flow by injecting crafted data that triggers the invalid memory access. This type of vulnerability falls under the CWE-125 weakness category, specifically representing an out-of-bounds read condition that allows attackers to access memory locations that should not be accessible. The flaw demonstrates characteristics consistent with memory corruption vulnerabilities that can be exploited through controlled data input manipulation, making it particularly dangerous in environments where UPX is used to process untrusted binary files.
The operational impact of CVE-2020-27797 extends beyond simple system crashes or instability, as it presents a significant vector for remote code execution attacks. Attackers can leverage this vulnerability by preparing malicious Mach-O files that, when processed by UPX 4.0.0, will trigger the memory corruption during the elf_lookup function execution. This creates a potential attack surface where adversaries can execute arbitrary code on systems running vulnerable versions of UPX, particularly in scenarios involving automated binary processing or security scanning tools that utilize UPX for compression analysis. The vulnerability affects systems where UPX is used to unpack or analyze Mach-O binaries, including macOS environments and systems that process such files through automated security workflows.
Mitigation strategies for CVE-2020-27797 require immediate version upgrades to UPX 4.0.1 or later, which contains the necessary patches to address the memory access validation issues. Organizations should implement comprehensive patch management procedures to ensure all instances of UPX are updated across their infrastructure, particularly in environments where binary processing occurs. Additional defensive measures include implementing strict file validation protocols that prevent processing of untrusted Mach-O files through UPX, utilizing sandboxing techniques when handling unknown binaries, and monitoring for anomalous behavior in systems that process compressed executables. The vulnerability also highlights the importance of input sanitization and memory safety practices in software development, aligning with ATT&CK technique T1059.007 for execution through command and scripting interpreter, where improper memory handling can lead to privilege escalation or code execution. Security teams should consider implementing network-based intrusion detection systems that can identify attempts to exploit this vulnerability through crafted binary files, while also ensuring that automated security scanning tools do not inadvertently trigger the vulnerability during analysis operations.