CVE-2019-20819 in PhantomPDF
Summary
by MITRE
An issue was discovered in Foxit Reader and PhantomPDF before 9.7. It allows stack consumption via nested function calls for XML parsing.
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Analysis
by VulDB Data Team • 10/22/2020
The vulnerability identified as CVE-2019-20819 represents a critical stack consumption flaw affecting Foxit Reader and PhantomPDF versions prior to 9.7. This issue manifests during XML parsing operations when the software encounters deeply nested function calls, leading to excessive stack memory consumption that can ultimately result in application crashes or potential exploitation scenarios. The vulnerability resides within the XML parser component of these PDF reading applications, which are widely used for document processing and viewing across enterprise and individual environments. The flaw demonstrates characteristics consistent with stack-based buffer overflow conditions, where recursive function calls consume stack space disproportionately, creating opportunities for denial of service attacks or more sophisticated exploitation techniques.
The technical implementation of this vulnerability exploits the XML parsing engine's handling of nested elements and function calls without adequate stack depth validation or recursion limits. When processing maliciously crafted XML documents containing deeply nested structures, the parser recursively invokes functions that consume stack memory at an exponential rate. This behavior aligns with CWE-770, which addresses the allocation of resources without proper limits, and CWE-121, which deals with stack-based buffer overflow conditions. The vulnerability demonstrates how improper input validation and lack of recursion depth controls can lead to resource exhaustion attacks that compromise application stability and availability.
From an operational standpoint, this vulnerability poses significant risks to organizations relying on Foxit Reader and PhantomPDF for document processing, particularly in environments where users may encounter untrusted XML content. The impact extends beyond simple application crashes to potentially enable more sophisticated attack vectors including privilege escalation or code execution depending on the specific implementation details and target environment. Security analysts should note that this vulnerability could be exploited by adversaries seeking to disrupt document processing workflows or gain unauthorized access to systems through compromised PDF reading applications. The attack surface includes any environment where these applications process XML content from external sources, making it particularly concerning for enterprise security teams managing document handling systems.
Organizations should prioritize immediate patching of affected Foxit Reader and PhantomPDF installations to version 9.7 or later, which includes fixes addressing the stack consumption issue. System administrators should implement network monitoring to detect potential exploitation attempts involving XML parsing operations and consider restricting XML content processing where possible. The mitigation strategy should include comprehensive vulnerability assessment of all systems running affected software versions and implementation of security controls that limit recursive function calls in XML processing components. Additionally, security teams should consider implementing application whitelisting policies to prevent execution of untrusted XML content through these vulnerable applications. This vulnerability highlights the importance of proper input validation and resource management in parsing libraries, particularly those handling structured data formats like xml that can be inherently recursive in nature.