CVE-2019-7156 in libdoc
Summary
by MITRE
In libdoc through 2019-01-28, calcFileBlockOffset in ole.c allows division by zero.
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Analysis
by VulDB Data Team • 05/06/2020
The vulnerability identified as CVE-2019-7156 affects the libdoc library version 2019-01-28 and earlier, specifically within the ole.c source file where the calcFileBlockOffset function exhibits a critical division by zero error. This flaw represents a classic software vulnerability that can lead to system instability and potential denial of service conditions when processing malformed or maliciously crafted Office document files. The issue occurs during the parsing of OLE (Object Linking and Embedding) structured storage files, which are commonly used in Microsoft Office document formats such as .doc, .xls, and .ppt files. When the function attempts to calculate file block offsets without proper validation of denominator values, it creates an opportunity for attackers to trigger a program crash or unexpected behavior through carefully constructed input data.
The technical implementation of this vulnerability stems from inadequate input validation within the calcFileBlockOffset function, which processes OLE file structures that contain information about how data blocks are organized within document files. When the function receives a zero value as a divisor during arithmetic operations used to determine block positioning, the program encounters a division by zero exception that typically results in an immediate crash or termination of the application process. This type of error falls under the common weakness enumeration CWE-369, which specifically addresses the condition where a division operation uses a zero value as the divisor, leading to runtime exceptions and potential system instability. The vulnerability is particularly concerning because it occurs during routine document processing operations, meaning that any user who opens a specially crafted malicious document could trigger the flaw without requiring special privileges or complex attack vectors.
The operational impact of CVE-2019-7156 extends beyond simple application crashes, as it can enable more sophisticated attack scenarios when combined with other vulnerabilities or when deployed in environments where document processing is automated. An attacker could leverage this vulnerability to perform denial of service attacks against systems that process Office documents, potentially affecting productivity software, document management systems, or email servers that automatically scan attachments. The vulnerability aligns with the ATT&CK framework's technique T1203, which covers "Exploitation for Client Execution" and can be used to establish footholds in target environments through malicious document delivery. Additionally, when combined with other memory corruption vulnerabilities, this division by zero condition could potentially lead to arbitrary code execution, making it a critical concern for enterprise security teams managing document processing infrastructure. The vulnerability affects not only end-user applications but also server-side systems that process documents for web applications, document conversion services, or automated content management platforms.
Mitigation strategies for CVE-2019-7156 should focus on immediate patching of the affected libdoc library version, as the vulnerability exists in the core document parsing functionality and cannot be effectively addressed through configuration changes alone. Organizations should prioritize updating to the latest stable version of libdoc where the division by zero condition has been properly handled through input validation and error checking mechanisms. System administrators should implement additional security controls including document scanning and validation before processing, network segmentation to limit exposure, and monitoring for unusual application behavior that might indicate exploitation attempts. The fix should incorporate proper validation of all arithmetic operations, particularly those involving file block calculations, to ensure that zero values are never used as denominators in division operations. Security teams should also consider implementing sandboxing or containerization for document processing applications to limit the potential impact of successful exploitation attempts, and conduct regular vulnerability assessments to identify similar issues in other third-party libraries used within their document processing pipelines.