CVE-2026-4947: Authentication Bypass Vulnerability

CVE-2026-4947 Overview

CVE-2026-4947 is an Insecure Direct Object Reference (IDOR) vulnerability affecting the signing invitation acceptance process. Under certain conditions, this vulnerability could allow an authenticated attacker to access or modify unauthorized resources by manipulating user-supplied object identifiers, potentially leading to forged signatures and compromising the integrity and authenticity of documents undergoing the signing process.

Critical Impact

This vulnerability could enable attackers to forge document signatures and compromise document integrity, undermining the trust and legal validity of digitally signed documents.

Affected Products

• Foxit document signing services (specific versions not disclosed)

Discovery Timeline

• 2026-04-01 - CVE-2026-4947 published to NVD
• 2026-04-01 - Last updated in NVD database

Technical Details for CVE-2026-4947

Vulnerability Analysis

This Insecure Direct Object Reference (IDOR) vulnerability exists within the signing invitation acceptance workflow. The vulnerability is classified under CWE-284 (Improper Access Control), indicating that the application fails to properly enforce authorization checks when processing requests that reference specific document or invitation objects.

When a user accepts a signing invitation, the application processes object identifiers submitted by the client. Due to insufficient authorization validation, an attacker with low-level authenticated access can manipulate these identifiers to reference objects belonging to other users. This broken access control enables unauthorized access to documents and signing workflows, potentially allowing signature forgery.

The network-accessible nature of this vulnerability means it can be exploited remotely by any authenticated user without requiring special privileges or user interaction.

Root Cause

The root cause of CVE-2026-4947 is insufficient authorization validation on referenced resources during request processing. The application fails to verify whether the authenticated user has legitimate access rights to the objects they are attempting to interact with through the signing invitation acceptance endpoint. This missing server-side authorization check allows attackers to bypass intended access controls by simply changing object identifier values in their requests.

Attack Vector

The attack leverages the network-accessible signing invitation acceptance endpoint. An authenticated attacker can intercept legitimate signing invitation requests and modify the object identifiers (such as document IDs, invitation IDs, or user references) to point to resources belonging to other users. Because the server does not properly validate authorization for the referenced objects, the malicious request is processed as if it were legitimate.

The exploitation flow involves:

1. An attacker authenticates to the document signing platform with valid credentials
2. The attacker initiates or intercepts a signing invitation acceptance request
3. The attacker modifies object identifiers in the request to reference another user's documents or signing sessions
4. The server processes the request without proper authorization validation
5. The attacker gains unauthorized access to view, modify, or forge signatures on documents they should not have access to

For technical details on this vulnerability, refer to the Foxit Security Bulletins.

Detection Methods for CVE-2026-4947

Indicators of Compromise

• Unusual patterns of signing invitation acceptance requests from single user accounts accessing multiple unrelated documents
• Authentication logs showing users accessing document resources outside their normal scope
• Audit trail anomalies where signatures appear on documents without corresponding legitimate invitation workflows

Detection Strategies

• Implement application-level logging to track all object identifier access patterns in signing workflows
• Monitor for sequential or enumerated object identifier access attempts that may indicate IDOR exploitation
• Deploy Web Application Firewall (WAF) rules to detect parameter manipulation attempts in signing endpoints
• Review access logs for authorization failures followed by successful access to different object IDs

Monitoring Recommendations

• Enable detailed audit logging for all document signing and invitation acceptance operations
• Configure alerts for users accessing an abnormally high number of distinct document objects
• Implement anomaly detection for authorization patterns in the signing invitation workflow
• Regularly review signing audit trails for signatures that lack corresponding legitimate invitation acceptance records

How to Mitigate CVE-2026-4947

Immediate Actions Required

• Review the Foxit Security Bulletins for patch availability and apply vendor-provided updates immediately
• Audit recent signing invitation acceptance logs for potential exploitation indicators
• Implement additional access controls or temporarily restrict access to signing invitation features if patching is delayed
• Review and validate the integrity of recently signed documents in affected systems

Patch Information

Foxit has addressed this vulnerability in their security updates. Organizations should consult the Foxit Security Bulletins for specific version information and download the latest patched version.

Workarounds

• Implement additional server-side authorization validation at the API gateway or reverse proxy level to verify user ownership of referenced objects
• Enable multi-factor authentication for signing operations to add an additional verification layer
• Temporarily restrict signing invitation acceptance to known trusted networks while awaiting patch deployment
• Implement rate limiting on signing invitation endpoints to slow potential enumeration attacks

If immediate patching is not possible, organizations should consider implementing defense-in-depth measures such as additional authorization checks at network boundaries and enhanced monitoring of signing workflows. Refer to the Foxit Security Bulletins for vendor-recommended mitigation guidance.