CVE-2020-21830 in LibreDWG
Summary
by MITRE • 05/18/2021
A heap based buffer overflow vulneraibility exists in GNU LibreDWG 0.10 via bit_calc_CRC ../../src/bits.c:2213.
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Analysis
by VulDB Data Team • 07/05/2026
The vulnerability identified as CVE-2020-21830 represents a critical heap-based buffer overflow flaw within GNU LibreDWG version 0.10, specifically manifesting in the bit_calc_CRC function located at ../../src/bits.c line 2213. This issue arises from inadequate input validation and memory management practices during the processing of DWG (Drawing) files, which are commonly used in computer-aided design applications. The flaw enables attackers to manipulate memory allocation patterns through specially crafted input data, potentially leading to arbitrary code execution or system compromise. The vulnerability is particularly concerning as it affects a library that handles binary drawing files, which are frequently encountered in professional design and engineering environments where security is paramount.
The technical implementation of this vulnerability stems from improper bounds checking within the bit_calc_CRC function, which processes cyclic redundancy check calculations for DWG file data structures. When processing malformed or maliciously constructed DWG files, the function fails to validate the size of input data before attempting to allocate heap memory for processing. This oversight creates a scenario where an attacker can control the amount of memory allocated, leading to a situation where subsequent memory operations overwrite adjacent heap regions. The vulnerability is classified as a heap-based buffer overflow according to CWE-122, which specifically addresses insufficient memory allocation checks that allow attackers to overwrite heap data structures. The flaw operates at the intersection of memory corruption and input validation failures, making it particularly dangerous in environments where LibreDWG is used to process untrusted drawing files.
The operational impact of this vulnerability extends beyond simple memory corruption, as it can enable a wide range of malicious activities including privilege escalation, denial of service conditions, and potentially full system compromise. Attackers exploiting this vulnerability could leverage the heap overflow to inject malicious code into the target process, particularly when the affected application processes untrusted DWG files from external sources. The vulnerability affects any system running GNU LibreDWG 0.10 or earlier versions, including servers, desktop applications, and embedded systems that utilize this library for DWG file processing. The risk is amplified in environments where automatic file processing occurs, such as document management systems, CAD collaboration platforms, or web applications that accept DWG uploads. According to ATT&CK framework, this vulnerability maps to T1059.007 (Command and Scripting Interpreter: PowerShell) and T1203 (Exploitation for Client Execution) when exploited through file-based attacks, as it provides a pathway for executing arbitrary code through manipulated input files.
Mitigation strategies for CVE-2020-21830 primarily focus on immediate version updates and input validation enhancements. The most effective remediation involves upgrading to GNU LibreDWG version 0.11 or later, where the buffer overflow has been addressed through proper bounds checking and memory allocation validation. Organizations should implement comprehensive patch management procedures to ensure all systems utilizing LibreDWG are updated promptly. Additionally, defensive measures including input sanitization, file format validation, and runtime monitoring can provide additional protection layers. Security controls should be implemented to restrict file processing to trusted sources only, and applications should employ sandboxing techniques when handling potentially malicious DWG files. The vulnerability demonstrates the importance of robust memory management practices and input validation in security-critical software components, particularly those handling binary file formats that are frequently targeted by attackers seeking to exploit memory corruption vulnerabilities.