CVE-2018-7436 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 pointer dereference of the parse_SST function.
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Analysis
by VulDB Data Team • 02/10/2023
The vulnerability identified as CVE-2018-7436 represents a critical heap-based buffer over-read condition within the FreeXL library version 1.0.4 and earlier. This flaw exists within the parse_SST function, which is responsible for parsing structured storage tables in excel files. The issue manifests when the library processes specially crafted excel files that contain malformed or maliciously constructed structured storage data. The buffer over-read occurs during pointer dereference operations where the application attempts to access memory locations beyond the allocated buffer boundaries, potentially leading to information disclosure or system instability.
The technical implementation of this vulnerability stems from inadequate input validation and memory management within the parse_SST function. When FreeXL encounters certain excel file structures, particularly those involving extended storage table formats, the function fails to properly bounds-check array accesses or validate the size of expected data structures. This allows an attacker to craft malicious excel files that cause the parser to read beyond allocated memory regions, resulting in unpredictable behavior. The vulnerability falls under CWE-125, which specifically addresses out-of-bounds read conditions, and demonstrates poor defensive programming practices in memory handling operations. The flaw represents a classic example of how improper validation of structured input data can lead to memory corruption vulnerabilities.
From an operational perspective, this vulnerability presents significant risks to systems that process excel files through the FreeXL library. Attackers could exploit this issue by delivering malicious excel files to systems running vulnerable versions of FreeXL, potentially leading to information disclosure from adjacent memory regions or system crashes. The impact extends beyond simple denial of service as the over-read could expose sensitive data such as cryptographic keys, user credentials, or system memory contents that might be accessible through the read operation. This vulnerability is particularly concerning in environments where excel processing is automated or where users can upload files to systems, as it could be leveraged for data exfiltration or further exploitation. The attack surface is broad given that FreeXL is used in various applications including database connectors, data analysis tools, and file processing systems.
The recommended mitigation strategy centers on immediate upgrade to FreeXL version 1.0.5 or later, which contains the necessary patches to address the buffer over-read condition. Organizations should conduct comprehensive vulnerability assessments to identify all systems running vulnerable versions of the library and prioritize their remediation. Additionally, implementing input validation controls at the application level can provide defense-in-depth measures, though the primary solution must be the library upgrade. Network segmentation and file upload restrictions can serve as temporary mitigations while full patches are deployed. Security monitoring should be enhanced to detect potential exploitation attempts through unusual file processing patterns or memory access anomalies. The vulnerability aligns with ATT&CK technique T1059.005 for execution through scripting and T1566 for initial access via malicious files, highlighting the importance of comprehensive endpoint protection and file validation mechanisms.