A critical vulnerability in OpnForm allows unauthenticated attackers to access or modify arbitrary form submissions due to predictable secret generation.

This vulnerability involves the use of predictable identifiers (CWE-340) due to an empty default salt in the Hashids implementation. This allows an unauthenticated attacker to compute valid submission hashes and interact with the submission-fetch and answer endpoints to steal or alter respondent data.

With a CVSS score of 9.1, this vulnerability poses a severe risk to data privacy and integrity. Unauthorized access to form submission data can lead to massive data breaches, while the ability to overwrite submissions undermines the reliability of the entire form-based collection process.

Immediate Action: Update OpnForm to version 2.0.2 or later to ensure proper salt configuration and secret generation.

Proactive Monitoring: Review application logs for a high volume of requests to submission-fetch endpoints from single sources, which may indicate automated data harvesting.

Compensating Controls: Deploy a Web Application Firewall (WAF) to detect and block suspicious patterns in requests targeting submission identifiers.

Public Exploit Available: Unknown.

This vulnerability is critical for any organization handling sensitive respondent data. Immediate patching to version 2.0.2 is required to prevent the unauthorized disclosure and manipulation of form submissions.