CVE-2018-7438 in FreeXL
Summary
by MITRE
An issue was discovered in FreeXL before 1.0.5. There is a heap-based buffer over-read in the parse_unicode_string function.
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Analysis
by VulDB Data Team • 02/10/2023
The vulnerability identified as CVE-2018-7438 represents a critical heap-based buffer over-read flaw within the FreeXL library version prior to 1.0.5. This issue manifests specifically within the parse_unicode_string function, where improper input validation leads to memory access violations that can be exploited by malicious actors. FreeXL is a lightweight library designed for reading excel files, particularly focusing on the .xls format, and is commonly integrated into various applications and systems for spreadsheet processing capabilities.
The technical flaw occurs when the parse_unicode_string function processes unicode character data without adequate bounds checking, allowing an attacker to craft specially malformed input that exceeds the allocated buffer boundaries. This over-read condition enables unauthorized memory access patterns that can potentially reveal sensitive data from adjacent memory locations or cause application crashes. The vulnerability stems from insufficient validation of input parameters and lacks proper boundary checks during string parsing operations, creating an exploitable condition that aligns with CWE-125: Buffer Under-read, which specifically addresses the issue of reading data past the end of a buffer.
The operational impact of this vulnerability extends across numerous systems that rely on FreeXL for excel file processing, including but not limited to database applications, reporting tools, and data analysis platforms. Attackers can leverage this flaw by constructing malicious excel files containing oversized unicode strings that trigger the buffer over-read condition when processed by vulnerable applications. This exploitation can result in information disclosure, application instability, or potentially more severe consequences depending on the specific implementation context. The vulnerability is particularly concerning because it operates at the parsing layer, meaning that any application utilizing FreeXL for file processing becomes susceptible to this memory access violation.
Mitigation strategies for CVE-2018-7438 primarily focus on immediate version updates to FreeXL 1.0.5 or later, which contain the necessary patches addressing the buffer over-read condition. System administrators should prioritize patch management across all affected environments and verify that applications using FreeXL have been updated to prevent exploitation. Additional defensive measures include implementing input validation controls, deploying network monitoring solutions to detect anomalous file processing patterns, and conducting thorough security assessments of applications that utilize this library. The vulnerability demonstrates the importance of proper memory management practices and input sanitization, aligning with ATT&CK technique T1059.007 for command and scripting interpreter usage in contexts where file processing libraries are involved. Organizations should also consider implementing application whitelisting policies and restricting file upload capabilities to reduce the attack surface for such exploitation scenarios.