CVE-2019-20817 in PhantomPDF
Summary
by MITRE
An issue was discovered in Foxit Reader and PhantomPDF before 9.7. It has a NULL pointer dereference.
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Analysis
by VulDB Data Team • 10/22/2020
The vulnerability identified as CVE-2019-20817 represents a critical NULL pointer dereference flaw affecting Foxit Reader and PhantomPDF software versions prior to 9.7. This issue resides within the document processing components of these PDF readers, where improper input validation leads to memory access violations when handling malformed or specially crafted PDF files. The vulnerability manifests during the parsing of specific PDF elements that trigger a scenario where a pointer variable remains uninitialized or set to NULL, yet the application attempts to dereference it without proper null checks. This class of vulnerability falls under CWE-476 which specifically addresses NULL pointer dereference conditions, making it a well-documented and dangerous weakness in software security architecture.
The technical exploitation of this vulnerability occurs when an attacker crafts a malicious PDF document containing malformed data structures that cause the affected software to attempt accessing memory at a NULL address. When the application encounters such input, it fails to implement proper error handling or validation routines, resulting in a crash or potential arbitrary code execution depending on the execution context. The flaw typically presents as an application crash or hang during document rendering, but in some configurations could potentially be leveraged for more sophisticated attacks. This vulnerability demonstrates poor defensive programming practices and highlights the importance of implementing robust input sanitization and null pointer validation throughout the application lifecycle.
The operational impact of CVE-2019-20817 extends beyond simple application instability, as it represents a potential gateway for more serious security breaches within enterprise environments where these PDF readers are commonly deployed. Organizations utilizing Foxit Reader or PhantomPDF for document processing, especially in high-security or compliance-sensitive contexts, face increased risk of service disruption and potential unauthorized access. The vulnerability affects both desktop and mobile versions of the software, making it particularly concerning for organizations with distributed user bases. Attackers could exploit this weakness to cause denial of service against legitimate users or potentially establish persistent access points within networks where these applications are widely used, aligning with ATT&CK technique T1203 for legitimate credentials and T1499 for network denial of service.
Mitigation strategies for this vulnerability require immediate patching of all affected Foxit Reader and PhantomPDF installations to version 9.7 or later, which includes proper null pointer validation and input sanitization routines. Organizations should implement strict document validation policies and consider deploying sandboxed environments for PDF processing to isolate potential exploitation attempts. Network administrators should monitor for suspicious PDF file transfers and consider implementing web application firewalls or content filtering solutions to block potentially malicious documents. Additionally, security teams should conduct comprehensive vulnerability assessments to identify any other applications or systems that might be similarly affected by similar NULL pointer dereference issues, following the principle of least privilege and implementing proper input validation across all software components. The remediation process should include thorough testing of patched versions to ensure that the vulnerability is fully resolved without introducing regressions in functionality.