CVE-2026-5941: Foxit PDF Editor Buffer Overflow Flaw

CVE-2026-5941 Overview

CVE-2026-5941 is a high-severity vulnerability in Foxit PDF Editor and PDF Reader that stems from parsing logic flaws in the handling of form field hierarchies. When processing malformed PDF documents, non-signature data can be misidentified as valid signatures, leading to invalid memory writes and program crashes during internal data structure construction. This improper input validation vulnerability (CWE-20) requires user interaction but can be exploited locally without authentication.

Critical Impact

Attackers can craft malicious PDF documents that, when opened by a victim, cause invalid memory writes potentially leading to integrity compromise and denial of service through application crashes.

Affected Products

• Foxit PDF Editor (all affected versions)
• Foxit PDF Reader (all affected versions)

Discovery Timeline

• 2026-04-27 - CVE-2026-5941 published to NVD
• 2026-04-29 - Last updated in NVD database

Technical Details for CVE-2026-5941

Vulnerability Analysis

The vulnerability exists within the PDF parsing engine of Foxit PDF Editor and PDF Reader applications. When the parser encounters form field hierarchies within a PDF document, it attempts to identify and process signature fields as part of standard document handling. However, due to improper input validation in the parsing logic, specially crafted malformed form field structures can cause the parser to incorrectly classify non-signature data as valid signature objects.

This misclassification triggers incorrect memory operations when the application attempts to construct internal data structures based on the misidentified signature data. The result is invalid memory writes that can corrupt program state and cause application crashes. The vulnerability requires that a user open a maliciously crafted PDF file, making it a local attack vector with user interaction required.

Root Cause

The root cause of CVE-2026-5941 is improper input validation (CWE-20) within the form field hierarchy parsing routines. The parsing logic fails to properly validate the structure and type of form field data before processing it as signature information. This lack of validation allows malformed data to bypass type checking mechanisms and be processed as valid signature objects, ultimately leading to memory corruption when the application attempts to use this data to build internal structures.

Attack Vector

The attack vector for this vulnerability is local and requires user interaction. An attacker would need to craft a malicious PDF document containing specially malformed form field hierarchies designed to trigger the parsing logic flaw. The attacker must then convince a victim to open the malicious PDF document using a vulnerable version of Foxit PDF Editor or PDF Reader. Successful exploitation does not require the attacker to have any special privileges on the target system.

The exploitation mechanism involves embedding malformed form field structures within a PDF document that appear valid enough to pass initial parsing but contain specially crafted data that causes the signature identification logic to misclassify non-signature data. When this misclassified data is processed during internal data structure construction, the resulting invalid memory writes can crash the application or potentially allow for further exploitation.

Detection Methods for CVE-2026-5941

Indicators of Compromise

• Unexpected crashes of Foxit PDF Editor or PDF Reader applications when opening PDF documents
• Application error logs indicating memory access violations or heap corruption during PDF parsing
• PDF documents with malformed or unusual form field hierarchies in the document structure

Detection Strategies

• Monitor for repeated crashes of FoxitPDFEditor.exe or FoxitPDFReader.exe processes, especially when correlated with PDF document access
• Implement file inspection rules to detect PDF documents with anomalous form field structures or unusually deep hierarchy nesting
• Deploy endpoint detection solutions capable of identifying memory corruption exploitation patterns in PDF reader applications

Monitoring Recommendations

• Enable crash reporting and memory dump collection for Foxit PDF applications to capture potential exploitation attempts
• Monitor file access patterns for PDF documents from untrusted sources, particularly email attachments or downloads
• Configure SentinelOne agents to alert on suspicious behavior patterns in Foxit PDF applications including unexpected memory operations

How to Mitigate CVE-2026-5941

Immediate Actions Required

• Update Foxit PDF Editor and PDF Reader to the latest patched versions available from the vendor
• Advise users to avoid opening PDF documents from untrusted or unknown sources until patches are applied
• Consider temporarily disabling or restricting access to Foxit PDF applications in high-security environments
• Enable Protected View or Safe Mode features if available in the application to reduce exploitation risk

Patch Information

Foxit has released security updates to address this vulnerability. Organizations should consult the Foxit Security Bulletins page for the latest patch information and download links for updated versions of Foxit PDF Editor and PDF Reader. It is recommended to apply these updates as soon as possible to mitigate the risk of exploitation.

Workarounds

• Configure email gateways to quarantine or scan PDF attachments before delivery to end users
• Implement application whitelisting to prevent execution of potentially malicious PDF documents through alternative viewers
• Use browser-based PDF viewing where possible as an alternative to desktop PDF reader applications
• Restrict user permissions to prevent installation of vulnerable software versions

# Verify installed Foxit PDF Reader/Editor version
# Windows: Check via registry or application properties
reg query "HKLM\SOFTWARE\Foxit Software\Foxit PDF Editor" /v Version
reg query "HKLM\SOFTWARE\Foxit Software\Foxit PDF Reader" /v Version