CVE-2020-21529 in fig2dev
Summary
by MITRE • 09/17/2021
fig2dev 3.2.7b contains a stack buffer overflow in the bezier_spline function in genepic.c.
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Analysis
by VulDB Data Team • 09/22/2021
The vulnerability CVE-2020-21529 represents a critical stack buffer overflow flaw in fig2dev version 3.2.7b, specifically within the bezier_spline function located in the genepic.c source file. This issue arises from improper input validation and memory management practices during the processing of graphical vector data files. The fig2dev utility serves as a converter tool that transforms files from the xfig format into various output formats including PostScript, PDF, and SVG, making it widely used in graphic design and document preparation workflows across multiple operating systems and platforms. The vulnerability manifests when the software processes malformed or specially crafted input files containing bezier curve data, leading to unauthorized memory access patterns that can result in arbitrary code execution or system crashes.
The technical root cause of this vulnerability stems from a classic stack buffer overflow condition where the bezier_spline function fails to properly bounds-check input parameters before copying data into fixed-size stack buffers. According to CWE-121, this represents a stack-based buffer overflow vulnerability that occurs when a program writes more data to a buffer than it can hold, typically due to inadequate input validation mechanisms. The flaw allows attackers to manipulate the program flow by overwriting adjacent stack memory locations, potentially enabling privilege escalation or remote code execution depending on the execution context. The vulnerability is particularly concerning because it exists in a utility that processes graphical input files, making it susceptible to exploitation through social engineering attacks where users might inadvertently open malicious vector graphics files.
The operational impact of CVE-2020-21529 extends beyond simple denial-of-service conditions to encompass serious security implications for systems running affected versions of fig2dev. Attackers could exploit this vulnerability by crafting malicious xfig files containing oversized bezier curve data that triggers the buffer overflow during conversion processes. When executed in environments where fig2dev is used for automated processing or in web applications that accept user-uploaded graphics, this vulnerability creates significant attack surface opportunities. The exploitability of this vulnerability is enhanced by the fact that fig2dev is commonly installed on development workstations, servers, and cloud environments where graphic processing is routine. This makes the vulnerability particularly dangerous in enterprise environments where automated build systems or document processing pipelines might be compromised.
Mitigation strategies for CVE-2020-21529 should focus on immediate patching of affected systems, implementing input validation controls, and adopting defensive programming practices. Organizations should prioritize updating to fig2dev version 3.2.7c or later, which contains the necessary fixes for this buffer overflow vulnerability. Additionally, implementing proper input sanitization measures including bounds checking, memory allocation validation, and stack canary implementations can significantly reduce the risk of exploitation. System administrators should also consider implementing sandboxing techniques and restricting execution privileges for fig2dev processes to limit potential damage from successful exploits. From an ATT&CK framework perspective, this vulnerability aligns with techniques such as T1059.007 (Command and Scripting Interpreter: PowerShell) and T1203 (Exploitation for Client Execution) when exploited in automated attack scenarios, emphasizing the need for comprehensive security controls including network segmentation, access controls, and continuous monitoring of system processes.