CVE-2026-3774: PDF JavaScript Information Disclosure Flaw

CVE-2026-3774 Overview

CVE-2026-3774 is an information exposure vulnerability affecting PDF processing applications that allow JavaScript and document/print actions to manipulate form fields, annotations, or optional content groups (OCGs) during critical operations. The vulnerability exists because script-driven updates executed via WillPrint/DidPrint actions are not fully covered by the existing redaction, encryption, and printing logic, potentially causing sensitive content to remain unremoved or unencrypted.

Critical Impact

Under specific document structures and user workflows, sensitive content may remain exposed after redaction operations, appear unencrypted despite encryption attempts, or produce printed output that differs from what was reviewed on screen—potentially leading to inadvertent disclosure of confidential information.

Affected Products

• PDF applications supporting JavaScript and document/print actions (specific products not disclosed in CVE data)
• Applications implementing WillPrint/DidPrint action handlers
• PDF processors with OCG and annotation manipulation capabilities

Discovery Timeline

• 2026-04-01 - CVE-2026-3774 published to NVD
• 2026-04-01 - Last updated in NVD database

Technical Details for CVE-2026-3774

Vulnerability Analysis

This vulnerability represents an information exposure flaw (CWE-200) in how PDF applications handle JavaScript execution timing relative to security-critical operations. The core issue lies in the interaction between document actions and the redaction/encryption/printing subsystems.

PDF documents can contain embedded JavaScript that executes at specific trigger points, including document events like WillPrint and DidPrint. These scripts have the capability to modify document content programmatically—updating form field values, toggling annotation visibility, or switching optional content groups on or off.

The vulnerability manifests when these script-driven modifications occur in a timing window that falls outside the scope of security operations. For instance, a malicious document could configure a DidPrint action to restore previously redacted content immediately after the printing logic has processed the document, but before the final output is generated.

Root Cause

The root cause stems from incomplete coverage of JavaScript-triggered document modifications within the application's security workflow. The redaction, encryption, and printing logic processes document content at a specific point in time, but does not account for subsequent modifications that may occur through document actions. This creates a race condition-like scenario where the security state captured during processing becomes stale by the time the operation completes.

The trust boundary between document content and embedded scripts is insufficiently enforced, allowing script execution to occur in contexts where it can undermine security operations that users believe have been applied.

Attack Vector

This is a local attack vector requiring user interaction. An attacker must craft a malicious PDF document containing:

1. Sensitive content configured to be hidden or redacted
2. JavaScript or document actions (WillPrint/DidPrint) designed to modify content visibility
3. Specific document structures that exploit the timing gap in security processing

The attack requires the victim to open the malicious document and perform a security-critical operation such as redaction, encryption, or printing. The victim believes the operation has succeeded based on their screen review, but the actual output may differ.

For technical implementation details, refer to the Foxit Security Bulletin.

Detection Methods for CVE-2026-3774

Indicators of Compromise

• PDF documents containing JavaScript with WillPrint, DidPrint, WillSave, or DidSave actions
• Documents with multiple optional content groups (OCGs) that toggle visibility during events
• Form fields or annotations with event-triggered scripts that modify content
• Discrepancies between on-screen document appearance and printed/exported output

Detection Strategies

• Implement static analysis of PDF documents to identify embedded JavaScript and document actions before processing
• Monitor for documents containing combinations of redactable content and document-level scripts
• Compare cryptographic hashes of document content before and after security operations to detect unexpected modifications
• Log all JavaScript execution events during redaction, encryption, and print operations for forensic review

Monitoring Recommendations

• Enable verbose logging for PDF processing operations to capture JavaScript execution timing
• Implement alerts for documents attempting to execute scripts during security-critical operations
• Monitor for user reports of discrepancies between expected and actual document output
• Track documents that trigger multiple content modifications during single operations

How to Mitigate CVE-2026-3774

Immediate Actions Required

• Disable JavaScript execution in PDF applications when performing redaction or encryption operations
• Configure PDF applications to flatten documents before applying security operations
• Implement a review workflow that compares final output against expected content
• Consider using PDF/A format for sensitive documents as it prohibits JavaScript

Patch Information

Consult the Foxit Security Bulletin for vendor-specific patch information and security updates addressing this vulnerability.

Workarounds

• Disable all JavaScript and document actions in PDF application preferences before processing sensitive documents
• Use the "Print to PDF" function and verify the resulting document matches expectations before distribution
• Flatten PDF documents to remove all interactive elements before applying redaction or encryption
• Manually verify that sensitive content is fully removed by examining the raw PDF structure after security operations
• Consider alternative PDF applications that process security operations atomically without JavaScript execution windows

# Configuration example for disabling JavaScript in PDF processing
# Note: Exact commands vary by application

# For command-line PDF tools, use --no-javascript flag
pdf-processor --no-javascript --flatten-before-redact input.pdf output.pdf

# Verify no JavaScript remains in processed document
pdf-analyze --check-scripts output.pdf