CVE-2020-27787 in UPX
Summary
by MITRE • 08/18/2022
A Segmentaation fault was found in UPX in invert_pt_dynamic() function in p_lx_elf.cpp. An attacker with a crafted input file allows invalid memory address access that could lead to a denial of service.
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Analysis
by VulDB Data Team • 04/11/2025
The vulnerability identified as CVE-2020-27787 represents a critical segmentation fault within the UPX (Ultimate Packer for eXecutables) compression utility, specifically manifesting in the invert_pt_dynamic() function located within the p_lx_elf.cpp source file. This flaw constitutes a classic buffer over-read condition that occurs during the processing of malformed executable files, creating a scenario where the application fails to properly validate memory access patterns during decompression operations. The issue arises from insufficient input validation mechanisms that allow an attacker to craft malicious input files that trigger improper memory handling within the ELF (Executable and Linkable Format) processing pipeline.
The technical implementation of this vulnerability stems from improper boundary checking within the dynamic page table inversion logic that UPX employs when processing Linux ELF executables. When the invert_pt_dynamic() function processes specially crafted input, it attempts to access memory addresses that fall outside the legitimate bounds of allocated memory regions, resulting in a segmentation fault that terminates the application process. This memory access violation represents a direct violation of memory safety principles and falls under the CWE-125 vulnerability category, which specifically addresses out-of-bounds read conditions. The flaw demonstrates a fundamental weakness in the input sanitization process where the compression utility fails to properly validate the structure and content of ELF headers before attempting to manipulate page table entries.
From an operational perspective, this vulnerability presents a significant denial of service risk that can be exploited by adversaries to disrupt legitimate system operations. The attack vector requires an adversary to craft a malicious executable file that, when processed by UPX for decompression or repacking, triggers the segmentation fault. This creates a scenario where automated systems relying on UPX for executable management could be rendered unavailable, potentially affecting software distribution channels, security scanning tools, or any system that utilizes UPX for package management. The impact extends beyond simple service interruption as it can also affect the integrity of the software supply chain, particularly in environments where UPX is used for automated processing of third-party executables.
The vulnerability aligns with several ATT&CK framework techniques, particularly those related to privilege escalation and execution through malicious file manipulation. The flaw can be leveraged as part of broader attack chains where adversaries first compromise a software distribution channel to inject malicious executables, then use the UPX vulnerability to ensure that legitimate security tools fail during processing. This creates a stealthy attack vector that can bypass traditional detection mechanisms while simultaneously disrupting defensive operations. Organizations utilizing UPX in their security infrastructure should consider this vulnerability as a potential entry point for sophisticated attacks that exploit the compression utility's role in automated security workflows.
Mitigation strategies for CVE-2020-27787 primarily focus on immediate software updates and input validation enhancements. The most effective remediation involves upgrading to UPX versions that contain patched implementations of the invert_pt_dynamic() function with proper memory boundary checks and input validation. Additionally, organizations should implement strict file validation procedures that prevent unknown or untrusted executables from being processed through UPX compression utilities. Network-level controls such as file type filtering and sandboxing mechanisms can provide additional layers of protection against exploitation attempts. The vulnerability also underscores the importance of implementing robust memory safety practices in compression and decompression utilities, particularly those handling untrusted input from diverse sources.