CVE-2020-21834 in LibreDWG
Summary
by MITRE • 05/18/2021
A null pointer deference issue exists in GNU LibreDWG 0.10 via get_bmp ../../programs/dwgbmp.c:164.
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Analysis
by VulDB Data Team • 05/22/2021
The vulnerability identified as CVE-2020-21834 represents a critical null pointer dereference flaw within GNU LibreDWG version 0.10, specifically manifesting in the dwgbmp.c source file at line 164. This issue arises during the processing of drawing files and particularly affects the get_bmp function which handles bitmap conversion operations. The flaw occurs when the software attempts to access a memory location that has not been properly initialized or allocated, creating a condition where a null pointer reference can lead to application termination or potential system instability.
The technical implementation of this vulnerability stems from inadequate input validation and memory management practices within the LibreDWG library. When processing certain AutoCAD drawing files or bitmap formats, the get_bmp function fails to properly validate pointer assignments before dereferencing them, resulting in a null pointer exception. This type of vulnerability falls under CWE-476 which specifically addresses null pointer dereference conditions in software implementations. The flaw demonstrates poor defensive programming practices where the software does not adequately check for null return values from memory allocation functions or file parsing operations.
From an operational standpoint, this vulnerability presents significant risks to organizations relying on GNU LibreDWG for CAD file processing and conversion. Attackers could exploit this weakness by crafting malicious drawing files that trigger the null pointer dereference during bitmap generation, potentially causing denial of service conditions or application crashes. The impact extends beyond simple service disruption as this vulnerability could be leveraged in broader attack chains where system stability is compromised, affecting workflows that depend on reliable CAD processing capabilities. The vulnerability's exploitation requires minimal privileges and could be automated, making it particularly dangerous in environments where automated file processing occurs.
Mitigation strategies for CVE-2020-21834 should prioritize immediate patching of the affected GNU LibreDWG version 0.10 to the latest available release that contains the fix for this null pointer dereference issue. Organizations should implement input validation measures that sanitize all drawing file inputs before processing, particularly focusing on bitmap conversion operations. Additionally, deploying defensive programming practices such as mandatory null pointer checks and proper error handling should be enforced throughout the application's codebase. Network segmentation and access controls can provide additional layers of protection by limiting exposure to potentially malicious file uploads. This vulnerability aligns with ATT&CK technique T1203 which covers exploitation of software vulnerabilities for privilege escalation and system compromise. Regular security assessments and code reviews should be conducted to identify similar null pointer dereference patterns that could exist in other components of the software ecosystem, ensuring comprehensive protection against similar threats.