CVE-2019-20805 in UPX
Summary
by MITRE
p_lx_elf.cpp in UPX before 3.96 has an integer overflow during unpacking via crafted values in a PT_DYNAMIC segment.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 04/11/2025
The vulnerability identified as CVE-2019-20805 resides within the UPX unpacking functionality, specifically in the p_lx_elf.cpp module of UPX versions prior to 3.96. This issue manifests during the unpacking process when processing ELF files that contain crafted values within the PT_DYNAMIC segment. The integer overflow occurs when the unpacker attempts to handle maliciously constructed segment values that exceed the expected range for integer calculations, creating a potential exploitation vector for attackers seeking to compromise systems running vulnerable UPX versions.
The technical flaw stems from inadequate input validation and overflow protection mechanisms within the ELF file parsing logic. When the UPX unpacker encounters a PT_DYNAMIC segment with manipulated values, it performs arithmetic operations that can cause integer overflow conditions. This vulnerability is particularly concerning because it operates at the unpacking stage of the UPX compression process, meaning it can be triggered when attempting to decompress maliciously crafted files that have been compressed with UPX. The integer overflow can lead to unpredictable behavior including memory corruption, which may result in denial of service conditions or potentially enable code execution under specific circumstances.
The operational impact of this vulnerability extends beyond simple denial of service scenarios. Attackers could potentially leverage this integer overflow to execute arbitrary code on systems that process or decompress malicious files compressed with UPX. This creates a significant risk for organizations that rely on UPX for software distribution, as a single compromised file could lead to widespread system compromise. The vulnerability affects any system running UPX versions before 3.96, including those that use UPX for legitimate software compression and distribution purposes. The attack surface is broad as UPX is commonly used in various software packages and applications, making this a widespread concern for system administrators and security professionals.
Mitigation strategies for CVE-2019-20805 primarily involve upgrading to UPX version 3.96 or later, which contains the necessary patches to address the integer overflow condition. Organizations should conduct comprehensive inventory assessments to identify all systems running vulnerable UPX versions and prioritize patching efforts accordingly. Additionally, implementing strict file validation procedures for compressed files and monitoring for unusual unpacking behaviors can help detect potential exploitation attempts. The vulnerability aligns with CWE-190, which specifically addresses integer overflow conditions, and could potentially map to ATT&CK technique T1059.007 for execution through decompressed payloads, highlighting the need for layered security approaches including endpoint detection and response capabilities to monitor for suspicious decompression activities and potential exploitation attempts.
This vulnerability demonstrates the critical importance of proper input validation and integer handling in security-critical software components. The issue underscores the necessity of thorough testing and validation of decompression and unpacking routines, particularly when dealing with potentially malicious inputs that could be used to manipulate internal data structures. Security teams should also consider implementing network-based detection measures that can identify and block known malicious UPX-compressed files, while maintaining awareness of other similar vulnerabilities that may exist in compression and archiving utilities that could serve as attack vectors for similar integer overflow conditions.