CVE-2020-28636 in libcgal
Summary
by MITRE • 03/05/2021
A code execution vulnerability exists in the Nef polygon-parsing functionality of CGAL libcgal CGAL-5.1.1. An oob read vulnerability exists in Nef_S2/SNC_io_parser.h SNC_io_parser::read_sloop() slh->twin() An attacker can provide malicious input to trigger this vulnerability.
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Analysis
by VulDB Data Team • 03/28/2021
The vulnerability CVE-2020-28636 represents a critical code execution flaw within the Computational Geometry Algorithms Library (CGAL) version 5.1.1, specifically within its Nef polygon-parsing functionality. This issue resides in the SNC_io_parser::read_sloop() method located in the Nef_S2/SNC_io_parser.h file, where an out-of-bounds read condition occurs during the processing of polygonal data structures. The vulnerability stems from improper input validation and memory access handling when parsing Nef polyhedra, which are used to represent planar subdivisions with holes and complex topological relationships. The flaw manifests when the slh->twin() operation attempts to access memory beyond the allocated bounds of the input data structure, creating a potential pathway for arbitrary code execution.
The technical implementation of this vulnerability involves the manipulation of polygonal input data that undergoes parsing through the Nef_S2 framework's SNC (Shell-Network-Cell) representation system. When the parser encounters malformed or specially crafted input, the read_sloop() function fails to properly validate array indices before accessing the twin() relationship of halfedges within the data structure. This out-of-bounds read can lead to information disclosure, memory corruption, and ultimately remote code execution depending on the attack vector and system configuration. The vulnerability aligns with CWE-125, which describes out-of-bounds read conditions, and represents a classic example of how geometric algorithms can be exploited through improper memory management during input parsing operations. The ATT&CK framework categorizes this as a code execution vulnerability that could be leveraged through malicious input delivery, potentially enabling privilege escalation or system compromise.
The operational impact of CVE-2020-28636 extends across various applications that rely on CGAL's computational geometry capabilities, particularly those involving geometric processing, computer graphics, CAD systems, and geographic information systems. Attackers can exploit this vulnerability by crafting malicious polygonal input files or data streams that trigger the out-of-bounds read during parsing operations. The vulnerability affects systems where CGAL is used for processing untrusted input, making it particularly dangerous in web applications, file processing services, and automated geometric computation pipelines. The exploitation requires minimal privileges and can result in complete system compromise, making it a high-severity threat. Organizations using CGAL libraries in production environments face significant risk, as the vulnerability can be triggered through various input channels including file uploads, network data processing, or API interactions that involve polygonal data manipulation.
Mitigation strategies for CVE-2020-28636 primarily involve immediate patching of affected CGAL versions to 5.1.2 or later, which contains the necessary fixes for the out-of-bounds read condition. System administrators should also implement input validation and sanitization measures for any polygonal data processing pipelines, particularly those involving external or untrusted sources. Network segmentation and access controls can help limit the potential impact of exploitation, while monitoring systems should be deployed to detect anomalous geometric processing patterns that might indicate exploitation attempts. Additionally, organizations should conduct thorough vulnerability assessments of their CGAL-dependent applications and implement proper memory safety checks during input processing. The fix addresses the root cause by ensuring proper bounds checking in the SNC_io_parser::read_sloop() function, preventing the out-of-bounds memory access that previously enabled code execution. Security teams should also consider implementing sandboxing techniques for geometric processing components and establishing incident response procedures specifically tailored to handle code execution vulnerabilities in computational geometry libraries.