CVE-2017-11626 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 four 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-2017-11626 represents a critical stack-consumption issue within the QPDF library version 6.0.0, specifically affecting the QPDFTokenizer::resolveLiteral function located in QPDFTokenizer.cc. This flaw manifests as an infinite loop condition that occurs after four consecutive invocations of QPDFObjectHandle::parseInternal, creating a scenario where the stack memory consumption grows uncontrollably. The issue arises from inadequate input validation and loop termination conditions within the PDF parsing logic, allowing maliciously crafted PDF files to trigger excessive resource consumption that ultimately leads to system instability.
The technical implementation of this vulnerability stems from the improper handling of PDF tokenization processes within the QPDF library. When processing specially crafted PDF files, the QPDFTokenizer::resolveLiteral function enters a recursive or iterative loop that fails to properly terminate after the fourth consecutive call to QPDFObjectHandle::parseInternal. This creates a condition where the stack frames accumulate indefinitely, consuming system memory resources at an exponential rate. The vulnerability is classified as a stack overflow condition that can be exploited through carefully constructed PDF content that manipulates the parsing state machine. According to CWE-400, this represents an unchecked resource consumption vulnerability, while the ATT&CK framework categorizes this under privilege escalation and denial of service techniques.
The operational impact of CVE-2017-11626 extends beyond simple denial of service, as it can potentially lead to complete system resource exhaustion and application crashes across any software that relies on the affected QPDF library. Systems processing untrusted PDF files become vulnerable to this attack vector, including document management systems, email servers, web applications, and security scanning tools. The vulnerability is particularly dangerous in automated processing environments where PDF files are handled without proper validation, as attackers can craft malicious documents that trigger the infinite loop condition during routine document processing. This makes the vulnerability exploitable in various attack scenarios including web-based attacks, email attachments, and file upload vulnerabilities.
Mitigation strategies for CVE-2017-11626 require immediate patching of the QPDF library to version 6.0.1 or later, which includes fixes for the stack consumption issue in the QPDFTokenizer::resolveLiteral function. Organizations should implement input validation measures that limit the complexity and size of PDF files processed, particularly when handling untrusted content. Network defenders should deploy intrusion detection systems that can identify suspicious PDF file patterns and implement sandboxing techniques for PDF processing. Additionally, application developers should consider implementing timeout mechanisms and stack depth monitoring when processing PDF documents. The vulnerability demonstrates the importance of proper resource management in parsing libraries and highlights the need for comprehensive testing of edge cases in file format parsers. Security teams should also monitor for similar vulnerabilities in other PDF processing libraries and ensure that all dependencies are regularly updated to prevent exploitation of known stack consumption flaws.