Authentication Bypass in Zimbra Collaboration Suite

Executive Summary

CVE-2026-93637 is a GraphQL authentication rate-limit bypass in Zimbra Collaboration Suite 10.1.0 through 10.1.21. It allows unauthenticated attackers to bypass Zimbra's source-IP-based failed login counter by using GraphQL aliases to send multiple authentication attempts in a single HTTP request. This bypasses the SOAP failure handler that normally increments the counter, enabling brute-force password attacks without triggering lockouts or rate limiting.

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Detection Guidance

Monitor for unusual GraphQL authentication traffic patterns, such as multiple authentication attempts within single HTTP requests or repeated failed logins without IP-based rate limiting triggers. Check Zimbra logs for GraphQL authentication endpoints receiving high volumes of requests compared to SOAP endpoints.

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Impact Analysis

Attackers can exploit this to perform brute-force password attacks on Zimbra accounts without detection. This increases the risk of unauthorized account access, data breaches, or further exploitation of the compromised accounts. The vulnerability reduces network overhead for attackers by allowing thousands of password guesses in one request.

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Compliance Impact

This vulnerability could weaken compliance with GDPR and HIPAA by allowing unauthorized access attempts to go undetected due to the bypass of rate-limiting and account lockout mechanisms. Uncontrolled brute-force attacks may expose sensitive data, violating confidentiality requirements under these regulations.

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Mitigation Strategies

Apply the latest Zimbra Collaboration Suite patches if available. Temporarily disable GraphQL authentication endpoints if not required. Implement additional rate limiting at the network or application level for GraphQL requests. Monitor for brute-force attempts and block suspicious IPs.

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