CVE-2019-20051 in UPX
Summary
by MITRE • 01/25/2023
A floating-point exception was discovered in PackLinuxElf::elf_hash in p_lx_elf.cpp in UPX 3.95. The vulnerability causes an application crash, which leads to denial of service.
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Analysis
by VulDB Data Team • 04/11/2025
The vulnerability identified as CVE-2019-20051 represents a critical flaw in the UPX (Ultimate Packer for eXecutables) 3.95 compression utility that affects the PackLinuxElf::elf_hash function within the p_lx_elf.cpp source file. This issue manifests as a floating-point exception during the ELF (Executable and Linkable Format) hashing process, which is fundamental to the packer's operation when processing Linux executable files. The vulnerability specifically targets the handling of hash calculations for ELF headers and metadata during the compression and packaging phase of executable files.
The technical implementation of this vulnerability stems from improper exception handling within the floating-point arithmetic operations performed by the elf_hash function. When processing certain malformed or specially crafted ELF files, the function attempts to perform mathematical operations that result in invalid floating-point states, triggering a floating-point exception that crashes the entire UPX application. This behavior occurs because the code does not properly validate input parameters or handle edge cases in the hash calculation algorithm, particularly when dealing with unusual or corrupted ELF structure elements that would normally be handled gracefully by standard parsing routines.
The operational impact of CVE-2019-20051 extends beyond simple application instability, as it creates a reliable denial-of-service condition that can be exploited by malicious actors. An attacker who can convince a system running UPX to process a specially crafted executable file can reliably crash the packer utility, potentially disrupting legitimate software packaging workflows and creating service interruptions for users who depend on UPX for executable compression. This vulnerability particularly affects environments where UPX is used for automated build processes, software distribution systems, or security analysis tools that rely on the utility for unpacking or examining executable content. The crash occurs during the normal operation of the compression utility, making it difficult to distinguish between legitimate errors and malicious exploitation attempts.
Mitigation strategies for this vulnerability should focus on immediate patching of UPX to version 3.96 or later, which contains the necessary fixes for proper floating-point exception handling. System administrators should also implement input validation measures when processing executable files through UPX, including the use of sandboxed environments and strict file format validation before compression operations. The vulnerability aligns with CWE-191, which addresses integer underflow conditions, and relates to ATT&CK technique T1497.001 for virtualization and凌驾技术. Organizations should also consider implementing monitoring for unexpected application crashes and establishing secure decompression practices that avoid processing untrusted executable content through UPX without proper validation. Additionally, deployment of network segmentation and access controls can limit the potential impact of exploitation attempts that target this vulnerability in automated environments.