CVE-2021-36080 in LibreDWG
Summary
by MITRE • 07/01/2021
GNU LibreDWG 0.12.3.4163 through 0.12.3.4191 has a double-free in bit_chain_free (called from dwg_encode_MTEXT and dwg_encode_add_object).
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Analysis
by VulDB Data Team • 07/04/2021
The vulnerability identified as CVE-2021-36080 represents a critical memory corruption issue within the GNU LibreDWG library version range 0.12.3.4163 through 0.12.3.4191. This library serves as a parser and writer for drawing files in the dwg format, which is commonly used in computer-aided design applications. The flaw manifests as a double-free condition that occurs during the processing of MTEXT entities within CAD drawings, specifically when the bit_chain_free function is invoked from dwg_encode_MTEXT and dwg_encode_add_object routines. This type of vulnerability falls under the category of memory safety errors and is classified as CWE-415, representing an attempt to free memory that has already been freed, creating a potential avenue for arbitrary code execution or denial of service attacks.
The technical implementation of this vulnerability involves the improper management of memory resources within the LibreDWG library's handling of MTEXT objects, which are multi-line text entities commonly found in CAD drawings. When processing these objects, the library calls the bit_chain_free function twice on the same memory block, leading to a state where freed memory is accessed or modified by subsequent operations. This double-free condition creates a scenario where an attacker could potentially manipulate the heap layout and achieve arbitrary code execution. The vulnerability is particularly concerning because it occurs during the encoding process of CAD files, meaning that any application using LibreDWG for processing or generating CAD documents could be exposed to this risk.
The operational impact of CVE-2021-36080 extends beyond simple denial of service to potentially enable remote code execution in vulnerable applications. Systems that process untrusted CAD files, such as CAD viewers, design collaboration platforms, or automated document processing systems, could be compromised when they utilize the affected LibreDWG library versions. This vulnerability aligns with ATT&CK technique T1203, which involves exploitation of software vulnerabilities through memory corruption, and represents a significant risk for organizations relying on CAD file processing workflows. The double-free condition could be exploited through carefully crafted CAD files that trigger the vulnerable code paths, making this a potential attack vector for adversaries seeking to compromise systems handling design documentation.
Mitigation strategies for CVE-2021-36080 primarily involve upgrading to a patched version of the GNU LibreDWG library, specifically versions beyond 0.12.3.4191 where the double-free condition has been resolved. System administrators and developers should conduct immediate inventory checks to identify all applications using the vulnerable library versions and implement patch management procedures. Additionally, input validation and sanitization measures should be enhanced when processing CAD files, including implementing sandboxing mechanisms and restricting file processing to trusted sources. The vulnerability demonstrates the importance of proper memory management practices and highlights the necessity of thorough code reviews and automated testing for memory safety issues, particularly in libraries that handle complex file format processing. Organizations should also consider implementing network segmentation and monitoring for suspicious file processing activities that might indicate exploitation attempts against this vulnerability.