Open Redirect Vulnerability in Cotonti CMS

Executive Summary

CVE-2026-100523 is an open redirect vulnerability in Cotonti CMS version 1.0.0. The issue is in the message.php file where the redirect parameter is base64-decoded without validating the domain. This allows unauthenticated attackers to craft malicious links with encoded external URLs that redirect users to arbitrary sites via meta refresh tags, enabling phishing attacks.

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Detection Guidance

Check Cotonti CMS version 1.0.0 for the message.php file. Look for base64-decoded redirect parameters without domain validation. Inspect meta refresh tags in user messages for external URLs. Review session handling in common.php for improper input validation.

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Impact Analysis

This vulnerability could allow attackers to trick users into visiting malicious websites through phishing links. Users might unknowingly enter sensitive information on fake sites, leading to account takeovers or malware infections. It could also be used to bypass security controls or deliver malicious payloads.

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Compliance Impact

This vulnerability could lead to unauthorized data access or disclosure, violating GDPR's data protection principles and HIPAA's security requirements. Organizations may face compliance violations, fines, or reputational damage if user data is compromised through phishing attacks exploiting this flaw.

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Mitigation Strategies

Upgrade Cotonti CMS to a patched version. Apply fixes from pull request #1908. Add CSRF tokens to forms, validate redirects with cot_url_check(), escape output to prevent XSS, and harden file uploads. Disable allowed classes in unserialize calls.

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