CVE-2020-21840 in LibreDWG
Summary
by MITRE • 05/18/2021
A heap based buffer overflow vulnerability exits in GNU LibreDWG 0.10 via bit_search_sentinel ../../src/bits.c:1985.
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Analysis
by VulDB Data Team • 05/22/2021
The heap-based buffer overflow vulnerability identified as CVE-2020-21840 resides within GNU LibreDWG version 0.10, specifically in the bit_search_sentinel function located in the ../../src/bits.c file at line 1985. This vulnerability represents a critical security flaw that can potentially allow attackers to execute arbitrary code or cause application crashes through malformed input processing. The issue manifests when the application processes certain DWG file formats that contain crafted data structures, leading to memory corruption in the heap allocation region.
This vulnerability falls under the Common Weakness Enumeration category CWE-121, which classifies heap-based buffer overflows as a fundamental memory safety issue. The flaw occurs when the bit_search_sentinel function fails to properly validate input boundaries before writing data to heap-allocated memory regions. The function processes bit-level data structures that are commonly found in AutoCAD DWG files, which are widely used in engineering and architectural design. When an attacker provides a maliciously crafted DWG file with oversized or malformed bit sequences, the function attempts to write beyond the allocated heap buffer, resulting in memory corruption that can be exploited for code execution or denial of service attacks.
The operational impact of this vulnerability extends beyond simple application instability, as it can be leveraged by attackers to gain unauthorized system access or disrupt critical infrastructure operations. Systems that process or convert DWG files, including CAD software, document management systems, and engineering workflows, become potential attack vectors. The vulnerability is particularly concerning because DWG files are commonly shared across organizations and may be processed automatically by various applications, increasing the attack surface. Additionally, the heap overflow can lead to information disclosure through memory corruption, potentially exposing sensitive data or system information.
Mitigation strategies for CVE-2020-21840 should focus on immediate patching of the GNU LibreDWG library to version 0.11 or later, where the buffer overflow has been addressed through proper input validation and boundary checking mechanisms. Organizations should implement defensive programming practices including stack canaries, address space layout randomization, and heap-based memory protection features to reduce exploitability. Input validation should be strengthened at multiple levels, including file format validation, size checking, and boundary verification before any heap allocation occurs. Network segmentation and access controls should limit exposure to systems processing DWG files, while regular security assessments should monitor for similar vulnerabilities in other libraries and applications processing binary data formats. The vulnerability also highlights the importance of following secure coding practices as outlined in the ATT&CK framework's software development security domain, particularly focusing on memory safety and input validation controls to prevent similar heap-based buffer overflow scenarios.