CVE-2017-2924 in FreeXL
Summary
by MITRE
An exploitable heap-based buffer overflow vulnerability exists in the read_legacy_biff 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-2017-2924 represents a critical heap-based buffer overflow within the FreeXL 1.0.3 library, specifically within the read_legacy_biff function. This flaw resides in the handling of Microsoft Excel file format parsing, where the library fails to properly validate input data when processing legacy BIFF (Binary Interchange File Format) structures. The vulnerability stems from inadequate bounds checking mechanisms that allow maliciously crafted XLS files to overflow allocated heap memory buffers, potentially leading to arbitrary code execution.
The technical implementation of this vulnerability involves the manipulation of structured binary data within Excel files that follow the older BIFF format specifications. When FreeXL processes these files, the read_legacy_biff function attempts to parse and interpret various data structures without sufficient validation of array boundaries or buffer sizes. This deficiency creates a scenario where attacker-controlled input data can overwrite adjacent memory locations, corrupting heap metadata and potentially allowing an attacker to manipulate program execution flow through memory corruption techniques.
The operational impact of this vulnerability extends beyond simple memory corruption, as it enables remote code execution capabilities when a victim opens a maliciously crafted XLS file through an application that utilizes the vulnerable FreeXL library. This presents significant risk in enterprise environments where users may inadvertently open malicious attachments or documents, particularly in phishing campaigns or targeted attacks. The vulnerability affects any application that relies on FreeXL for Excel file parsing, including various office suites, document management systems, and data processing applications that support legacy Excel formats.
Security researchers have classified this vulnerability according to CWE-121, which describes heap-based buffer overflow conditions, and it aligns with ATT&CK technique T1203, which covers exploitation of remote services through file format vulnerabilities. The attack vector requires social engineering to deliver the malicious XLS file to a target system, but once executed, the vulnerability can provide full system compromise. Mitigation strategies include immediate patching of FreeXL to version 1.0.4 or later, implementing strict file validation controls, deploying sandboxing mechanisms for document processing, and educating users about the risks of opening untrusted Excel files. Organizations should also consider network-based intrusion detection systems that can identify and block suspicious file transfers containing known malicious patterns.