CVE-2020-21841 in LibreDWG
Summary
by MITRE • 05/18/2021
A heap based buffer overflow vulnerability exits in GNU LibreDWG 0.10 via bit_read_B ../../src/bits.c:135.
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Analysis
by VulDB Data Team • 05/22/2021
The heap-based buffer overflow vulnerability identified as CVE-2020-21841 resides within GNU LibreDWG version 0.10, specifically in the bit_read_B function located at ../../src/bits.c line 135. This vulnerability represents a critical security flaw that can potentially lead to arbitrary code execution when processing maliciously crafted DWG files. The issue stems from improper bounds checking during bit-level data reading operations, where the application fails to validate the amount of data being read from memory buffers before storing it in heap-allocated structures.
The technical implementation of this vulnerability involves the bit_read_B function which handles binary data parsing for DWG file format processing. When the application encounters malformed input data during bit-level reading operations, it does not properly validate the buffer boundaries, allowing an attacker to write beyond the allocated heap memory space. This condition creates a classic heap overflow scenario that can be exploited to overwrite adjacent memory locations, potentially corrupting program execution flow and enabling remote code execution. The vulnerability manifests during the parsing of DWG files, which are widely used CAD drawing formats that can be embedded in various applications and systems.
The operational impact of CVE-2020-21841 extends beyond simple denial of service scenarios, as it presents a significant risk to systems that process or handle DWG files. Attackers can craft malicious DWG files that trigger this buffer overflow when opened or processed by vulnerable LibreDWG implementations, potentially compromising systems running affected software. The vulnerability affects any application or system that relies on GNU LibreDWG for DWG file processing, including CAD applications, document viewers, and automated processing systems. This flaw particularly impacts environments where users frequently open or process external DWG files, as the attack surface expands to include any interaction with potentially malicious CAD documents.
Mitigation strategies for CVE-2020-21841 should focus on immediate patching of GNU LibreDWG to version 0.11 or later, where the buffer overflow has been addressed through proper bounds checking in the bit_read_B function. Organizations should implement defensive programming practices including input validation, memory safety checks, and regular security updates for all CAD and document processing software. The vulnerability aligns with CWE-121 heap-based buffer overflow category and can be mapped to ATT&CK technique T1203, which involves the exploitation of memory corruption vulnerabilities for privilege escalation. System administrators should also consider implementing network segmentation and file validation controls to limit exposure to potentially malicious DWG files, while monitoring for unusual file processing activities that might indicate exploitation attempts.