CVE-2015-9252 in QPDF
Summary
by MITRE
An issue was discovered in QPDF before 7.0.0. Endless recursion causes stack exhaustion in QPDFTokenizer::resolveLiteral() in QPDFTokenizer.cc, related to the QPDF::resolve function in QPDF.cc.
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Analysis
by VulDB Data Team • 02/06/2023
The vulnerability identified as CVE-2015-9252 represents a critical stack exhaustion flaw within the QPDF library version 7.0.0 and earlier. This issue manifests in the QPDFTokenizer::resolveLiteral() function located in QPDFTokenizer.cc, where improper handling of certain PDF structures leads to infinite recursive calls that rapidly consume system stack memory. The problem is particularly concerning because it occurs during the normal processing of PDF documents, making it exploitable through routine document parsing operations. The vulnerability is directly linked to the QPDF::resolve function in QPDF.cc, which serves as the core mechanism for resolving PDF object references and handling complex document structures.
The technical root cause of this vulnerability stems from inadequate input validation and recursion bounds checking within the PDF tokenization and resolution processes. When QPDF encounters specific malformed or crafted PDF constructs, the tokenizer enters an infinite loop where resolveLiteral() repeatedly calls itself without proper termination conditions. This recursive behavior is exacerbated by the library's handling of complex object references and cross-reference structures that may contain circular or self-referencing elements. The stack exhaustion occurs because each recursive call consumes stack space, and without proper safeguards, the system quickly runs out of available stack memory. This type of vulnerability aligns with CWE-674, which categorizes "Uncontrolled Recursion" as a common weakness leading to denial of service conditions.
The operational impact of CVE-2015-9252 extends beyond simple denial of service scenarios, as it can affect any application or system that relies on QPDF for PDF processing. When exploited, this vulnerability can cause applications to crash or become unresponsive, effectively rendering them unusable until restarted. The vulnerability is particularly dangerous in server environments where PDF processing is a common operation, as it can be leveraged to perform denial of service attacks against web applications, document management systems, and other services that process user-uploaded PDF files. Attackers can craft malicious PDF documents that trigger the recursive behavior, potentially causing cascading failures in systems that process large volumes of documents. This vulnerability directly maps to ATT&CK technique T1499.004, which describes "Endpoint Denial of Service" through resource exhaustion attacks.
Mitigation strategies for CVE-2015-9252 primarily focus on upgrading to QPDF version 7.0.0 or later, where the recursion bounds have been properly implemented and stack exhaustion protections have been added. System administrators should also implement input validation and sanitization measures to detect and reject malformed PDF files before they reach the QPDF processing layer. Additionally, deploying memory monitoring and resource limiting mechanisms can help prevent complete system crashes when this vulnerability is exploited. Organizations using QPDF in production environments should conduct thorough testing of the updated library to ensure compatibility with existing workflows while maintaining robust security postures. The fix implemented in version 7.0.0 demonstrates proper defensive programming practices that include maximum recursion depth checks and iterative processing alternatives to prevent stack overflow conditions.