CVE-2017-2923 in FreeXL
Summary
by MITRE
An exploitable heap based buffer overflow vulnerability exists in the 'read_biff_next_record function' of FreeXL 1.0.3. A specially crafted XLS file can cause a memory corruption resulting in remote code execution. An attacker can send malicious XLS file to trigger this vulnerability.
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Analysis
by VulDB Data Team • 03/07/2023
The vulnerability identified as CVE-2017-2923 represents a critical heap-based buffer overflow within the FreeXL library version 1.0.3, specifically within the read_biff_next_record function. This flaw resides in the handling of Microsoft Excel file formats, where the library processes the BIFF (Binary Interchange File Format) records that constitute the internal structure of xls files. The vulnerability stems from insufficient bounds checking during the parsing of malformed xls files, creating an exploitable condition where an attacker can craft a malicious file that triggers memory corruption when processed by vulnerable applications.
The technical implementation of this vulnerability follows a classic heap overflow pattern where the application fails to validate the size of data being read from the input file before copying it into a fixed-size buffer allocated on the heap. When the read_biff_next_record function processes a specially crafted XLS file, it encounters a record header that specifies a length exceeding the allocated buffer space, leading to adjacent memory corruption. This type of vulnerability maps directly to CWE-121, which describes heap-based buffer overflow conditions where insufficient bounds checking allows attackers to overwrite adjacent heap memory locations. The overflow can potentially overwrite function pointers, return addresses, or other critical control data structures within the heap allocation, providing an attacker with the opportunity to redirect program execution flow.
The operational impact of this vulnerability extends beyond simple memory corruption, as it enables remote code execution when a victim application processes the malicious xls file through the vulnerable FreeXL library. This creates a significant risk for web applications, email clients, and document processing systems that utilize FreeXL for xls file parsing. The attack vector requires the victim to open or process the malicious file, which can occur through various delivery mechanisms including email attachments, web downloads, or file sharing platforms. The vulnerability affects any application that integrates FreeXL version 1.0.3 or earlier, making it particularly dangerous in environments where multiple applications depend on this library for spreadsheet processing functionality.
Security mitigations for CVE-2017-2923 primarily focus on immediate remediation through version updates, as the vulnerability was addressed in FreeXL version 1.0.4 and subsequent releases. Organizations should prioritize updating their FreeXL installations and conducting comprehensive vulnerability assessments to identify all systems that may be impacted by this flaw. Additionally, implementing input validation controls and sandboxing mechanisms can provide defense-in-depth protection, ensuring that even if an attacker successfully exploits the vulnerability, the impact remains contained. Network-based protections such as email filtering and web application firewalls can help prevent the delivery of malicious xls files to end users. From an ATT&CK framework perspective, this vulnerability aligns with techniques involving initial access through malicious files and privilege escalation through code execution, emphasizing the need for comprehensive endpoint protection and user education to prevent successful exploitation attempts.