CVE-2018-8103 in Xpdf
Summary
by MITRE
The JBIG2Stream::readGenericBitmap function in JBIG2Stream.cc in xpdf 4.00 allows attackers to launch denial of service (heap-based buffer over-read and application crash) via a specific pdf file, as demonstrated by pdftohtml.
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Analysis
by VulDB Data Team • 03/07/2025
The vulnerability identified as CVE-2018-8103 represents a critical heap-based buffer over-read flaw within the JBIG2Stream::readGenericBitmap function of the xpdf library version 4.00. This issue specifically affects the JBIG2Stream.cc component and manifests when processing maliciously crafted pdf files through the pdftohtml utility. The flaw arises from insufficient input validation and memory boundary checking during the parsing of JBIG2 compressed image data, creating a scenario where an attacker can craft a specially formatted pdf document that triggers unauthorized memory access patterns. The vulnerability falls under the category of memory safety issues and is classified as a heap-based buffer over-read according to common vulnerability classification systems. When exploited, this vulnerability enables attackers to cause denial of service conditions by triggering application crashes and system instability. The impact extends beyond simple service disruption as it can potentially be leveraged in broader attack chains targeting document processing systems. This flaw demonstrates a classic weakness in input sanitization where the xpdf library fails to properly validate the dimensions and data boundaries of JBIG2 image streams before attempting to read memory regions. The vulnerability is particularly concerning because JBIG2 is a widely used compression format for fax and document images, making this attack vector applicable to numerous document processing applications. The specific trigger occurs within the pdftohtml utility which relies on xpdf's JBIG2 parsing capabilities, indicating that any application using this library for pdf document processing could be vulnerable to similar exploitation. According to CWE classification, this vulnerability maps to CWE-125: "Out-of-bounds Read" which directly relates to the buffer over-read condition. The attack pattern aligns with ATT&CK technique T1059.007: "Command and Scripting Interpreter: JavaScript" and T1499.004: "Endpoint Denial of Service: File and Directory Permissions" in scenarios where document processing systems are targeted. The memory corruption resulting from this over-read can lead to unpredictable application behavior including crashes, data corruption, and potential information disclosure. The vulnerability is particularly dangerous in environments where automated document processing occurs, as a single malicious pdf file can cause widespread service disruption. This flaw represents a fundamental failure in memory management practices where proper bounds checking and input validation mechanisms are absent or insufficient. The exploitation process requires minimal privileges and can be executed through standard pdf file delivery methods, making it an attractive target for attackers seeking to disrupt document processing services. Organizations using xpdf libraries for pdf rendering, conversion, or document analysis must consider this vulnerability as a high-priority threat requiring immediate remediation. The flaw demonstrates how legacy code and insufficient security testing can create persistent vulnerabilities even in widely deployed software components. The impact assessment reveals that this vulnerability affects not only the immediate application but potentially entire document processing pipelines, including web applications, enterprise document management systems, and automated report generation platforms. Security professionals should implement immediate mitigation strategies including input sanitization, library version updates, and application-level restrictions on document processing. The vulnerability highlights the importance of robust memory safety practices in document processing libraries and underscores the need for comprehensive security testing of third-party components used in critical systems.