CVE-2020-21815 in LibreDWG
Summary
by MITRE • 05/18/2021
A null pointer deference issue exists in GNU LibreDWG 0.10.2641 via output_TEXT ../../programs/dwg2SVG.c:114, which causes a denial of service (application crash).
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Analysis
by VulDB Data Team • 05/22/2021
The vulnerability identified as CVE-2020-21815 represents a critical null pointer dereference flaw within GNU LibreDWG version 0.10.2641 that specifically manifests in the dwg2SVG.c source file at line 114. This issue arises during the processing of CAD drawing files when the application attempts to dereference a null pointer, leading to an application crash that constitutes a denial of service condition. The vulnerability is particularly concerning as it occurs in the output_TEXT function which handles text rendering operations within the conversion process from DWG to SVG formats, making it a potential attack vector for malicious actors seeking to disrupt services that rely on this library.
From a technical perspective, the null pointer dereference vulnerability stems from inadequate input validation and error handling within the LibreDWG library's text processing routines. When the dwg2SVG.c module encounters certain malformed or incomplete DWG files, the code fails to properly check if a pointer variable contains a valid memory reference before attempting to access it. This failure typically occurs when the application expects a specific data structure or object to be present in memory but finds a null value instead, causing the program to terminate abruptly rather than gracefully handling the error condition. The vulnerability is classified under CWE-476 as a NULL Pointer Dereference, which is a well-documented weakness that represents a fundamental flaw in software error handling practices.
The operational impact of this vulnerability extends beyond simple application instability, as it creates a potential denial of service scenario that can affect any system or service utilizing GNU LibreDWG for CAD file processing. When exploited, the vulnerability can cause cascading failures in applications that depend on this library for converting CAD drawings to alternative formats, potentially disrupting engineering workflows, design processes, and automated document processing systems. The vulnerability is particularly dangerous in environments where LibreDWG is used as a backend component in web applications or automated systems that process large volumes of CAD files, as a single malicious or corrupted file could bring down entire processing pipelines. Attackers could exploit this weakness by crafting specially formatted DWG files that trigger the null pointer dereference during text rendering operations, making it a valuable vector for service disruption attacks.
Mitigation strategies for CVE-2020-21815 should focus on both immediate patching and defensive programming practices. The most effective solution involves upgrading to a patched version of GNU LibreDWG that addresses the null pointer dereference issue in the output_TEXT function. System administrators and developers should also implement robust input validation mechanisms that can detect and reject malformed DWG files before they reach the vulnerable code path. Additional defensive measures include implementing proper error handling and graceful degradation strategies, where applications can continue processing other elements of a file even when encountering problematic text elements. From an ATT&CK framework perspective, this vulnerability aligns with techniques related to denial of service and application vulnerability exploitation, making it relevant to both the T1499 and T1595 tactics that focus on disrupting services and exploiting software weaknesses. Organizations should also consider implementing sandboxing mechanisms for processing untrusted CAD files and establishing monitoring systems to detect unusual application crash patterns that might indicate exploitation attempts.