CVE-2017-9210 in QPDF
Summary
by MITRE
libqpdf.a in QPDF 6.0.0 allows remote attackers to cause a denial of service (infinite recursion and stack consumption) via a crafted PDF document, related to unparse functions, aka qpdf-infiniteloop3.
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Analysis
by VulDB Data Team • 12/07/2022
The vulnerability identified as CVE-2017-9210 affects QPDF version 6.0.0 and represents a critical denial of service flaw that can be exploited remotely through crafted PDF documents. This vulnerability specifically targets the libqpdf.a library component within the QPDF software suite, which is widely used for manipulating and converting PDF files. The flaw manifests as infinite recursion and excessive stack consumption, creating a condition where a specially crafted PDF document can trigger an unbounded recursive parsing process that consumes system resources until the application crashes or becomes unresponsive.
The technical root cause of this vulnerability lies within the unparse functions of the QPDF library implementation. When processing malformed PDF documents, these functions fail to properly validate recursive structures or implement adequate recursion depth limits. The vulnerability is categorized under CWE-674 which specifically addresses Uncontrolled Recursion, a well-known weakness that can lead to stack overflow conditions and system instability. The attack vector requires an adversary to craft a malicious PDF file that contains recursive structures or self-referential elements that the parser cannot handle gracefully, leading to the infinite recursion scenario.
From an operational impact perspective, this vulnerability creates significant risk for organizations that process untrusted PDF files through QPDF libraries. The denial of service condition can affect any system or application that relies on QPDF for PDF processing, including document management systems, email servers, web applications, and automated processing pipelines. The infinite recursion consumes memory and CPU resources rapidly, potentially causing system crashes, application hangs, or resource exhaustion that can be exploited for distributed denial of service attacks. This vulnerability particularly affects systems that automatically process or validate PDF files without proper input sanitization, as described in the ATT&CK framework's technique T1499 for Denial of Service.
Mitigation strategies for CVE-2017-9210 should focus on immediate patching of affected QPDF installations to version 6.0.1 or later where the recursion depth limits have been implemented. Organizations should also implement input validation measures that restrict PDF file sizes and complexity before processing, utilize sandboxed environments for PDF handling, and consider implementing rate limiting for PDF processing operations. Network-level defenses can include content filtering systems that scan PDF attachments for suspicious structures, while application-level protections should enforce proper recursion depth monitoring and resource allocation limits. The vulnerability highlights the importance of robust input validation and proper error handling in parsing libraries, aligning with security best practices outlined in the OWASP Top Ten and other industry security frameworks that emphasize the need for defensive programming techniques to prevent recursive parsing vulnerabilities.