CVE-2018-7437 in FreeXL
Summary
by MITRE
An issue was discovered in FreeXL before 1.0.5. There is a heap-based buffer over-read in a memcpy call of the parse_SST function.
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Analysis
by VulDB Data Team • 02/10/2023
The vulnerability identified as CVE-2018-7437 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_SST function where a memcpy operation executes without adequate bounds checking, creating an exploitable condition that can lead to memory corruption and potential arbitrary code execution. The FreeXL library serves as an open-source tool for reading excel files, particularly focusing on the legacy .xls format, making it a widely used component in various applications that process spreadsheet data.
The technical root cause of this vulnerability stems from insufficient input validation and memory management within the parse_SST function which handles the parsing of shared string tables in excel files. When processing malformed or specially crafted excel files, the function attempts to copy data using memcpy without verifying that the destination buffer can accommodate the requested data size, resulting in a buffer over-read condition. This flaw allows an attacker to read data from adjacent memory locations beyond the allocated buffer boundaries, potentially exposing sensitive information or enabling further exploitation techniques.
From an operational impact perspective, this vulnerability poses significant risks to systems utilizing FreeXL for processing excel files, particularly in environments where untrusted data is processed. The buffer over-read can lead to application crashes, information disclosure, or in more severe cases, arbitrary code execution depending on the specific memory layout and exploitation circumstances. Attackers can craft malicious excel files that trigger this condition when opened or processed by applications using the vulnerable FreeXL library, making it a valuable target for remote code execution attacks in web applications or file processing services.
The vulnerability aligns with CWE-125, which specifically addresses out-of-bounds read conditions in software systems, and can be mapped to ATT&CK technique T1059.007 for executing malicious code through file processing vulnerabilities. Organizations should prioritize updating to FreeXL version 1.0.5 or later to remediate this vulnerability, as the fix includes proper bounds checking and input validation mechanisms within the parse_SST function. Additional mitigations include implementing strict input validation for excel file processing, deploying sandboxing techniques for untrusted file analysis, and monitoring for suspicious file processing activities that could indicate exploitation attempts. Security teams should also consider implementing network segmentation and access controls to limit the potential impact of successful exploitation attempts targeting this vulnerability.