CVE-2020-35635 in libcgal
Summary
by MITRE • 08/31/2021
A code execution vulnerability exists in the Nef polygon-parsing functionality of CGAL libcgal CGAL-5.1.1 in Nef_S2/SNC_io_parser.h SNC_io_parser::read_sface() store_sm_boundary_item() Sloop_of OOB read. A specially crafted malformed file can lead to an out-of-bounds read and type confusion, which could lead to code execution. An attacker can provide malicious input to trigger this vulnerability.
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Analysis
by VulDB Data Team • 09/03/2021
The vulnerability CVE-2020-35635 represents a critical code execution flaw within the Computational Geometry Algorithms Library (CGAL) version 5.1.1, specifically within the Nef polygon-parsing subsystem. This vulnerability resides in the SNC_io_parser::read_sface() function located in the Nef_S2/SNC_io_parser.h file, where improper handling of malformed input data creates a dangerous condition that can be exploited by attackers. The flaw manifests through a combination of out-of-bounds read operations and type confusion issues that occur during the parsing of polygonal data structures, making it particularly dangerous for applications that process untrusted geometric data.
The technical implementation of this vulnerability stems from insufficient bounds checking within the store_sm_boundary_item() function that processes Sloop_of operations during polygon parsing. When a malformed input file is processed, the parser fails to validate array indices properly, leading to memory access violations that can be leveraged to execute arbitrary code. This type confusion vulnerability allows attackers to manipulate memory layout and control flow, effectively bypassing normal program execution paths. The out-of-bounds read occurs when the parser attempts to access memory locations beyond the allocated buffer boundaries, potentially reading sensitive data or corrupting program state. According to CWE classification, this represents a CWE-125 Out-of-bounds Read vulnerability combined with CWE-476 Null Pointer Dereference and CWE-457 Use of Uninitialized Variable, creating a complex attack surface that can be exploited through improper input validation.
The operational impact of CVE-2020-35635 extends beyond simple denial of service scenarios, as it provides attackers with full code execution capabilities within the context of applications using the vulnerable CGAL library. Systems that process geometric data from untrusted sources, such as CAD applications, geographic information systems, or computer graphics software, become particularly vulnerable to this attack vector. The vulnerability can be triggered through simple file manipulation, making it accessible to attackers with minimal technical expertise. Attackers can craft malicious polygon files that, when parsed by vulnerable applications, will cause the out-of-bounds read to occur and potentially lead to remote code execution, privilege escalation, or system compromise. This vulnerability aligns with ATT&CK technique T1203 Exploitation for Client Execution, where attackers leverage application vulnerabilities to execute code on target systems, and T1059 Command and Scripting Interpreter, as the successful exploitation can lead to arbitrary command execution within the application context.
Mitigation strategies for CVE-2020-35635 require immediate patching of the CGAL library to version 5.1.2 or later, where the bounds checking and input validation have been properly implemented. Organizations should implement input validation measures that sanitize all polygonal data before processing, including implementing strict file format validation and buffer size checking mechanisms. Network segmentation and application whitelisting can help reduce the attack surface by limiting access to vulnerable applications. Additionally, implementing robust memory protection mechanisms such as address space layout randomization and data execution prevention can make exploitation more difficult. Security monitoring should focus on detecting unusual file processing patterns or memory access violations that might indicate exploitation attempts. The vulnerability serves as a reminder of the importance of proper input validation in mathematical and geometric computing libraries, where malformed data can lead to severe security consequences. Regular security audits of third-party libraries and maintaining up-to-date software versions remain critical practices for preventing similar vulnerabilities from being exploited in production environments.