CVE-2021-38563 in Foxit
Summary
by MITRE • 08/12/2021
An issue was discovered in Foxit PDF Reader before 11.0.1 and PDF Editor before 11.0.1. It mishandles situations in which an array size (derived from a /Size entry) is smaller than the maximum indirect object number, and thus there is an attempted incorrect array access (leading to a NULL pointer dereference, or out-of-bounds read or write).
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Analysis
by VulDB Data Team • 08/16/2021
The vulnerability identified as CVE-2021-38563 represents a critical memory corruption flaw affecting Foxit PDF Reader and PDF Editor versions prior to 11.0.1. This issue stems from improper handling of PDF file structures during the parsing of indirect object arrays, specifically when processing the /Size entry within the cross-reference table. The flaw occurs when the parser encounters a situation where the declared array size is insufficient to accommodate the maximum indirect object number present in the document, creating a fundamental mismatch between expected and actual data structures.
The technical implementation of this vulnerability involves a classic buffer overflow condition that manifests through improper bounds checking during PDF object parsing. When the PDF reader processes a document containing a malformed /Size entry, it attempts to create an array structure that cannot accommodate all the indirect objects referenced within the file. This misalignment results in memory access violations where the application attempts to access memory locations beyond the allocated array boundaries. The vulnerability can lead to three distinct types of memory corruption: NULL pointer dereference, out-of-bounds read operations, or out-of-bounds write operations, each presenting different exploitation vectors and potential impacts.
From an operational standpoint, this vulnerability poses significant risks to end users and organizations relying on Foxit PDF applications for document processing and viewing. The memory corruption can result in application crashes, system instability, and potentially provide attackers with opportunities for arbitrary code execution. The nature of PDF processing makes this particularly dangerous as users commonly open documents from untrusted sources, creating numerous attack vectors through malicious PDF files. The vulnerability's impact extends beyond simple denial of service to potentially enabling more sophisticated attacks that could compromise entire systems.
Security practitioners should recognize this vulnerability as mapping to CWE-129, which specifically addresses insufficient validation of length fields, and CWE-787, covering out-of-bounds write operations. The flaw also aligns with ATT&CK technique T1203, which involves exploitation of software vulnerabilities for privilege escalation and system compromise. Organizations should prioritize immediate patching of affected Foxit applications to address this memory corruption issue, implementing additional controls such as PDF sandboxing and content filtering to reduce the risk of exploitation. The vulnerability underscores the critical importance of robust input validation and memory safety practices in document processing applications, particularly those handling untrusted binary data formats like PDF files.