CVE-2017-9209 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 QPDFObjectHandle::parseInternal, aka qpdf-infiniteloop2.
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Analysis
by VulDB Data Team • 12/07/2022
The vulnerability identified as CVE-2017-9209 represents a critical denial of service flaw within the QPDF library version 6.0.0, specifically affecting the libqpdf.a component. This issue manifests when processing specially crafted PDF documents that trigger infinite recursion during the parsing phase, leading to excessive stack consumption and ultimately system resource exhaustion. The vulnerability is rooted in the QPDFObjectHandle::parseInternal function which fails to properly validate recursive structures within PDF objects, creating a scenario where malicious input can cause the parser to enter an endless loop.
The technical exploitation of this vulnerability occurs through the manipulation of PDF document structures that contain recursive object references or malformed nested objects. When the QPDF library attempts to parse these crafted documents, the parseInternal method recursively processes object references without adequate depth checking or termination conditions. This results in the stack growing indefinitely until system resources are exhausted, causing the application to crash or become unresponsive. The flaw demonstrates characteristics consistent with CWE-674, which describes "Uncontrolled Recursion" in software systems where recursive calls lack proper termination conditions or depth limits.
From an operational perspective, this vulnerability presents significant risk to any system or application that relies on QPDF for PDF processing, including document management systems, web applications handling PDF uploads, and security scanning tools. Attackers can exploit this weakness by crafting malicious PDF files that, when processed by vulnerable applications, will consume excessive system resources and potentially cause service disruption. The impact extends beyond simple denial of service as it can be leveraged in broader attack campaigns targeting infrastructure dependencies that utilize the affected library. This vulnerability aligns with ATT&CK technique T1499.001 which covers "Endpoint Denial of Service" and demonstrates how improper input validation can lead to resource exhaustion attacks.
Mitigation strategies for CVE-2017-9209 should prioritize immediate patching of affected QPDF versions to 7.0.0 or later, where the recursive parsing logic has been properly constrained with depth limits and termination conditions. Organizations should also implement input validation measures at the application level, including setting timeouts for PDF processing operations and monitoring stack usage during parsing operations. Additional protective measures include deploying sandboxing techniques for PDF processing, implementing rate limiting on document uploads, and establishing monitoring protocols to detect unusual resource consumption patterns that may indicate exploitation attempts. Network segmentation and access controls should be reinforced to limit exposure of systems that process untrusted PDF content, while regular security assessments should verify that all dependencies are updated to secure versions that address this specific recursion vulnerability.