CVE-2020-21818 in LibreDWG
Summary
by MITRE • 05/18/2021
A heap based buffer overflow vulnerability exists in GNU LibreDWG 0.10.2641 via htmlescape ../../programs/escape.c:48.
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Analysis
by VulDB Data Team • 05/22/2021
The heap-based buffer overflow vulnerability identified as CVE-2020-21818 affects GNU LibreDWG version 0.10.2641 and specifically manifests in the htmlescape function within the escape.c file at line 48. 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 stems from improper memory management during HTML escaping operations, where insufficient bounds checking permits data to be written beyond the allocated heap buffer boundaries. Such vulnerabilities typically arise when developers fail to validate input lengths against allocated memory space, creating opportunities for attackers to manipulate memory layout and potentially execute malicious payloads.
The technical implementation of this vulnerability involves the htmlescape function processing input data that undergoes HTML entity encoding operations. When the function receives input that exceeds the predetermined buffer size, it continues writing data to adjacent heap memory locations without proper boundary enforcement. This heap overflow condition can corrupt adjacent memory structures, leading to unpredictable application behavior including crashes, data corruption, or more severe exploitation scenarios. The vulnerability is classified under CWE-121 Heap-based Buffer Overflow, which specifically addresses buffer overflow conditions where data is written beyond the boundaries of heap-allocated buffers. The attack surface is particularly concerning given that LibreDWG is used for processing dwg files, which are commonly exchanged between CAD applications and could serve as delivery mechanisms for malicious payloads.
From an operational perspective, this vulnerability poses significant risks to systems processing CAD files or documents that may contain maliciously crafted HTML escape sequences. Attackers could exploit this weakness by crafting specially formatted dwg files that trigger the vulnerable htmlescape function during file processing or conversion operations. The impact extends beyond simple application crashes to potentially enable privilege escalation or remote code execution depending on the execution context and system configuration. Organizations utilizing LibreDWG for document processing, CAD file conversion, or automated workflows face heightened risk of exploitation, particularly in environments where untrusted input is processed without proper sanitization. The vulnerability can be leveraged in supply chain attacks where malicious dwg files are distributed through legitimate channels, making detection and prevention challenging.
Mitigation strategies for CVE-2020-21818 should prioritize immediate patching of LibreDWG to version 0.10.2642 or later where the heap overflow has been addressed through proper bounds checking and memory allocation controls. System administrators should implement input validation and sanitization measures to prevent malformed HTML escape sequences from reaching the vulnerable function. The implementation of address space layout randomization, stack canaries, and other exploit mitigation techniques can provide additional defense layers. Organizations should also consider network segmentation and access controls to limit exposure of systems processing CAD files, particularly those that may encounter untrusted input. Regular security assessments and vulnerability scanning should be conducted to identify similar memory corruption issues in other components of the software stack. The ATT&CK framework categorizes this vulnerability under T1203 Exploitation for Client Execution when exploited in file processing contexts, emphasizing the need for comprehensive endpoint protection and user awareness training to prevent successful exploitation attempts.