CVE-2017-18183 in QPDF
Summary
by MITRE
An issue was discovered in QPDF before 7.0.0. There is an infinite loop in the QPDFWriter::enqueueObject() function in libqpdf/QPDFWriter.cc.
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Analysis
by VulDB Data Team • 02/06/2023
The vulnerability identified as CVE-2017-18183 represents a critical denial of service flaw within the QPDF software library, which is widely utilized for PDF processing and manipulation across various applications and systems. This issue affects versions prior to 7.0.0 and stems from a fundamental flaw in the QPDFWriter::enqueueObject() function located in the libqpdf/QPDFWriter.cc source file. The nature of this vulnerability allows an attacker to craft malicious PDF files that can trigger an infinite loop during the processing phase, effectively causing the application to hang indefinitely and consume excessive system resources.
The technical implementation of this vulnerability exploits the object queuing mechanism within the PDF writer component of QPDF. When processing certain malformed PDF structures, the enqueueObject() function enters a state where it continuously iterates through a loop without proper termination conditions. This infinite loop occurs during the object processing phase when the library attempts to organize and queue PDF objects for output generation. The flaw manifests specifically when the library encounters certain object relationships or cross-references that cause the internal queue management logic to fail, resulting in an unbounded execution cycle that can only be terminated by manual intervention or system resource exhaustion.
From an operational impact perspective, this vulnerability presents significant risks to systems that rely on QPDF for PDF processing, including web applications, document management systems, and automated PDF generation services. The infinite loop behavior can be exploited through crafted PDF files delivered via email attachments, web uploads, or file sharing systems, potentially leading to service disruption, resource exhaustion, and system instability. The vulnerability is particularly concerning because it can be triggered by simple PDF files without requiring complex exploitation techniques, making it accessible to attackers with minimal technical expertise. This makes it a prime candidate for abuse in distributed denial of service attacks or as part of broader attack chains targeting PDF processing capabilities.
The vulnerability aligns with CWE-835, which specifically addresses the issue of infinite loops in software implementations, and can be mapped to ATT&CK technique T1499.004, which covers network denial of service attacks. Organizations utilizing QPDF in their infrastructure should prioritize immediate patching to version 7.0.0 or later, as this represents the first release that contains the necessary fixes for this infinite loop condition. Additionally, implementing input validation and sanitization measures for PDF processing workflows can provide additional defense-in-depth layers. System administrators should also consider monitoring for unusual resource consumption patterns and implementing timeouts for PDF processing operations to mitigate potential exploitation scenarios. The fix implemented in version 7.0.0 addresses the root cause by introducing proper loop termination conditions and enhanced queue management logic within the QPDFWriter component, ensuring that object processing cannot enter indefinite execution states regardless of input complexity.