CVE-2017-12595 in QPDF
Summary
by MITRE
The tokenizer in QPDF 6.0.0 and 7.0.b1 is recursive for arrays and dictionaries, which allows remote attackers to cause a denial of service (stack consumption and segmentation fault) or possibly have unspecified other impact via a PDF document with a deep data structure, as demonstrated by a crash in QPDFObjectHandle::parseInternal in libqpdf/QPDFObjectHandle.cc.
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Analysis
by VulDB Data Team • 12/16/2022
The vulnerability identified as CVE-2017-12595 affects QPDF versions 6.0.0 and 7.0.b1, where the tokenizer implementation exhibits recursive behavior when processing arrays and dictionaries within PDF documents. This recursive design creates a fundamental flaw in the software's parsing mechanism that can be exploited by malicious actors to manipulate the application's execution flow. The tokenizer's recursive nature means that each nested structure within a PDF document triggers a new function call on the call stack, leading to exponential stack consumption as the nesting depth increases. This design pattern violates secure coding practices and represents a classic example of inadequate input validation and resource management.
The technical implementation of this vulnerability stems from the recursive function calls in QPDFObjectHandle::parseInternal located in libqpdf/QPDFObjectHandle.cc. When processing PDF documents containing deeply nested arrays or dictionaries, the recursive tokenizer consumes stack space at a rate proportional to the nesting depth rather than maintaining constant memory usage. This recursive approach creates a path for attackers to craft malicious PDF files with excessively deep data structures that will cause the application to exhaust available stack memory. The vulnerability manifests as either a denial of service condition through stack exhaustion leading to segmentation faults or potentially more severe impacts including arbitrary code execution depending on the system's memory layout and the specific conditions under which the stack overflow occurs.
The operational impact of this vulnerability extends beyond simple denial of service scenarios, as it provides attackers with a reliable method to disrupt PDF processing services and applications that depend on QPDF for document manipulation. Systems utilizing QPDF for PDF validation, conversion, or security scanning become vulnerable to targeted attacks that can render these services unavailable to legitimate users. The vulnerability affects any application or service that processes PDF documents through the affected QPDF versions, including web applications, document management systems, and security scanning tools that rely on QPDF for parsing PDF content. This makes the vulnerability particularly dangerous in enterprise environments where PDF processing is a common requirement for business operations and security workflows.
Mitigation strategies for CVE-2017-12595 should prioritize immediate patching of affected QPDF installations to version 7.0.0 or later where the recursive tokenizer has been replaced with an iterative implementation. Organizations should implement defensive measures such as setting stack limits on PDF processing services and implementing input validation to detect and reject PDF documents with suspiciously deep nesting structures. Additionally, network segmentation and application whitelisting can help limit the potential impact of exploitation attempts by restricting access to vulnerable systems. The vulnerability aligns with CWE-674, which describes "Uncontrolled Recursion" as a weakness that can lead to stack overflow conditions, and may map to ATT&CK technique T1059.007 for execution through command-line interfaces if exploited in certain contexts. Regular security assessments and dependency updates should be implemented to prevent similar recursive design flaws in other software components that may be susceptible to similar stack exhaustion attacks.