CVE-2017-11624 in QPDF
Summary
by MITRE
A stack-consumption vulnerability was found in libqpdf in QPDF 6.0.0, which allows attackers to cause a denial of service via a crafted file, related to the QPDFTokenizer::resolveLiteral function in QPDFTokenizer.cc after two consecutive calls to QPDFObjectHandle::parseInternal, aka an "infinite loop."
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Analysis
by VulDB Data Team • 12/14/2022
The vulnerability identified as CVE-2017-11624 represents a critical stack consumption issue within the libqpdf library component of QPDF version 6.0.0. This flaw manifests as a denial of service condition that can be triggered by crafting malicious PDF files designed to exploit specific parsing behaviors within the library. The vulnerability specifically targets the QPDFTokenizer::resolveLiteral function located in QPDFTokenizer.cc, which demonstrates how improper handling of input data can lead to system instability and resource exhaustion. The flaw operates through a sequence of operations that creates an infinite loop condition, consuming excessive stack memory and ultimately leading to application termination or system resource depletion.
The technical implementation of this vulnerability stems from the improper handling of consecutive calls to QPDFObjectHandle::parseInternal within the QPDFTokenizer::resolveLiteral function. When the library processes a specially crafted PDF file, the parsing routine enters an iterative state where it repeatedly calls the internal parsing functions without proper termination conditions. This behavior creates a stack-based infinite loop scenario where each recursive call consumes additional stack space, eventually exhausting the available stack memory allocation. The vulnerability demonstrates characteristics consistent with CWE-835, which addresses infinite loops or iterations without proper exit conditions, making it particularly dangerous in environments where resource constraints are critical.
From an operational impact perspective, this vulnerability poses significant risks to systems that rely on QPDF for PDF processing, including document management systems, web applications, and content filtering solutions. Attackers can exploit this weakness by submitting maliciously constructed PDF files to services that utilize libqpdf for parsing or validation, resulting in denial of service conditions that can disrupt legitimate operations. The vulnerability affects not only the immediate application but can also impact system stability, as the stack exhaustion can cause crashes or forced restarts of processes handling PDF documents. Organizations using QPDF 6.0.0 in production environments face potential service disruption and increased operational overhead due to the need for manual intervention when such attacks occur.
The exploitation of this vulnerability aligns with tactics described in the MITRE ATT&CK framework under the denial of service category, specifically targeting application stability and resource availability. Security professionals should consider implementing input validation and sanitization measures to prevent malformed PDF files from reaching the vulnerable parsing routines. Mitigation strategies include upgrading to QPDF versions that address this specific stack consumption issue, implementing resource limits on PDF processing services, and deploying automated monitoring to detect unusual stack consumption patterns. Additionally, organizations should conduct regular security assessments of their PDF processing workflows and ensure that all components within their document handling pipelines are properly updated to prevent exploitation of known vulnerabilities. The vulnerability serves as a reminder of the importance of proper resource management in parsing libraries and the need for robust termination conditions in recursive processing functions to prevent stack-based denial of service attacks.