CVE-2018-20650 in Poppler
Summary
by MITRE
A reachable Object::dictLookup assertion in Poppler 0.72.0 allows attackers to cause a denial of service due to the lack of a check for the dict data type, as demonstrated by use of the FileSpec class (in FileSpec.cc) in pdfdetach.
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Analysis
by VulDB Data Team • 06/22/2023
The vulnerability identified as CVE-2018-20650 represents a critical denial of service weakness within the Poppler PDF library version 0.72.0, specifically affecting the pdfdetach utility. This flaw stems from an insufficient type validation mechanism within the Object::dictLookup function, which is responsible for dictionary lookups in the PDF parsing process. The vulnerability manifests when the FileSpec class processes certain PDF files, failing to properly validate that dictionary data types are appropriate before attempting operations on them. This assertion failure occurs during the normal execution flow of pdfdetach when handling maliciously crafted PDF documents, creating an opportunity for attackers to disrupt service availability.
The technical root cause of this vulnerability aligns with CWE-691, which encompasses inadequate checks for dangerous operations on data structures. The flaw demonstrates a classic insufficient validation scenario where the code assumes that dictionary objects contain expected data types without performing proper type checking. The assertion failure in Object::dictLookup creates an immediate crash condition that terminates the pdfdetach process, effectively rendering the utility unavailable for legitimate use. This behavior constitutes a denial of service attack vector that can be exploited by any attacker who can provide a specially crafted PDF file to the vulnerable application, making it particularly dangerous in environments where automated PDF processing occurs.
The operational impact of CVE-2018-20650 extends beyond simple service disruption, as it can be leveraged to create persistent availability issues in systems that rely on Poppler for PDF handling. The vulnerability is particularly concerning in server environments where pdfdetach might be invoked programmatically, such as in document management systems, email processing pipelines, or automated PDF conversion services. Attackers could repeatedly submit malicious PDF files to cause continuous service interruptions, potentially leading to complete system unavailability. From an attacker perspective, this vulnerability maps to ATT&CK technique T1499.004, which involves network denial of service attacks targeting specific applications, and T1059.007, which involves command and script injection through file processing utilities.
Mitigation strategies for CVE-2018-20650 should focus on both immediate patching and operational hardening measures. The most effective solution involves upgrading to Poppler version 0.73.0 or later, where the vulnerability has been addressed through proper type validation in the Object::dictLookup function. Organizations should also implement input validation controls that filter or sanitize PDF files before processing them through Poppler utilities. Additional defensive measures include restricting access to pdfdetach functionality, implementing timeouts for PDF processing operations, and monitoring for unusual patterns of service disruption that might indicate exploitation attempts. Network segmentation and application whitelisting can further reduce the attack surface by limiting which systems can execute pdfdetach and access potentially malicious PDF content, thereby providing layered protection against this and similar denial of service vulnerabilities.