CVE-2018-18459 in Xpdf
Summary
by MITRE
The function DCTStream::getBlock in Stream.cc in Xpdf 4.00 allows remote attackers to cause a denial of service (NULL pointer dereference) via a crafted pdf file, as demonstrated by pdftoppm.
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Analysis
by VulDB Data Team • 03/07/2025
The vulnerability identified as CVE-2018-18459 represents a critical denial of service weakness within the Xpdf PDF processing library version 4.00. This flaw specifically manifests in the DCTStream::getBlock function located within the Stream.cc source file, where improper input validation leads to a NULL pointer dereference condition. The vulnerability is particularly concerning because it can be exploited remotely through the manipulation of crafted pdf files, making it accessible to attackers without requiring local system access or elevated privileges.
The technical exploitation of this vulnerability occurs when a malicious PDF file triggers the DCTStream::getBlock function to attempt dereferencing a NULL pointer during the decompression process of JPEG data streams within PDF documents. This condition arises from insufficient bounds checking and error handling within the JPEG decompression implementation, which fails to properly validate the structure and content of embedded JPEG images before attempting to process them. The flaw is classified under CWE-476 as a NULL pointer dereference, representing a common class of software vulnerabilities that can lead to application crashes and system instability.
The operational impact of this vulnerability extends beyond simple service disruption, as it affects the reliability and availability of PDF processing applications that depend on the Xpdf library. When exploited, the vulnerability causes applications like pdftoppm to crash immediately upon processing the malicious file, effectively rendering them unusable for legitimate document processing tasks. This denial of service condition can be particularly damaging in environments where PDF processing is critical, such as document management systems, automated print servers, or web applications that handle user-uploaded PDF content. The vulnerability affects all applications built on the Xpdf 4.00 library, including but not limited to pdftoppm, pdftotext, and various web-based PDF viewers that utilize this component.
Mitigation strategies for CVE-2018-18459 focus primarily on upgrading to patched versions of the Xpdf library, specifically versions 4.01 or later where the NULL pointer dereference has been addressed through improved input validation and error handling mechanisms. System administrators should prioritize patching affected applications that rely on the vulnerable library, particularly those handling untrusted PDF content from external sources. Additionally, implementing input sanitization measures such as PDF validation before processing, employing sandboxing techniques for PDF handling, and deploying network-based intrusion detection systems that can identify and block malicious PDF files can provide additional layers of protection. From an ATT&CK framework perspective, this vulnerability aligns with the technique T1203 - Exploitation for Client Execution and T1499.004 - Endpoint Denial of Service, as it enables adversaries to disrupt services through the manipulation of PDF file content. Organizations should also consider implementing application whitelisting policies and restricting the execution of PDF processing utilities from untrusted sources to minimize the attack surface. The vulnerability demonstrates the importance of robust input validation in multimedia processing libraries and highlights the need for comprehensive security testing of document parsing components that handle complex binary formats like JPEG within structured documents.