CVE-2015-2776 in FreeXL
Summary
by MITRE
The parse_SST function in FreeXL before 1.0.0i allows remote attackers to cause a denial of service (memory consumption) via a crafted shared strings table in a workbook.
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Analysis
by VulDB Data Team • 05/02/2022
The vulnerability identified as CVE-2015-2776 resides within the FreeXL library version prior to 1.0.0i, specifically within the parse_SST function that handles shared strings tables in workbook files. This flaw represents a classic denial of service vulnerability that can be exploited remotely by crafting malicious shared strings table data. The FreeXL library serves as an open-source tool for reading excel files and extracting data from them, making it a widely used component in various applications and systems that process spreadsheet data. When a maliciously constructed shared strings table is processed by the vulnerable parse_SST function, the library fails to properly validate or limit memory allocation during the parsing process, leading to excessive memory consumption that can ultimately result in system resource exhaustion and application crash.
The technical root cause of this vulnerability stems from inadequate input validation and memory management within the parse_SST function. When processing workbook files containing shared strings tables, the function does not properly validate the size or structure of the table data, allowing an attacker to craft input that causes the library to allocate excessive memory resources. This behavior aligns with CWE-772, which describes insufficient resource exhaustion protection, and represents a memory exhaustion attack vector that can be classified under the broader category of resource exhaustion vulnerabilities. The vulnerability is particularly concerning because it operates at the parsing level where the library processes external data without proper bounds checking, making it susceptible to malformed input that can cause uncontrolled memory growth.
The operational impact of this vulnerability extends beyond simple service disruption, as it can affect any system or application that relies on FreeXL for processing excel files. Attackers can exploit this vulnerability by creating specially crafted excel workbooks with malformed shared strings tables that, when processed by vulnerable applications, consume excessive memory resources. This can lead to system instability, application crashes, and potential denial of service for legitimate users who depend on these services. The remote exploitation capability means that attackers do not need physical access to the target system, making this vulnerability particularly dangerous in networked environments where excel files are frequently processed and shared. Systems running applications that use FreeXL for file processing, including web applications, data processing pipelines, and automated reporting systems, could be vulnerable to this attack vector.
Mitigation strategies for CVE-2015-2776 primarily focus on upgrading to FreeXL version 1.0.0i or later, which contains the necessary patches to address the memory consumption issue in the parse_SST function. Organizations should also implement input validation measures at the application level to sanitize excel file inputs before processing them through FreeXL, including setting memory limits and timeouts for file processing operations. Additionally, network segmentation and access controls should be implemented to limit exposure to potentially malicious files, and regular security assessments should be conducted to identify other vulnerable components that may be using the affected library. This vulnerability highlights the importance of proper resource management in parsing libraries and aligns with ATT&CK technique T1499.004, which covers network denial of service attacks, and demonstrates the critical need for robust input validation in data processing components to prevent resource exhaustion attacks.