CVE-2026-76183 in Tomcat
Summary
by MITRE • 09/23/2026
Authentication Bypass by Alternate Name vulnerability in Apache Tomcat allowed the security constraints for any WebSocket endpoint to be bypassed.
This issue affects Apache Tomcat: from 11.0.0-M1 through 11.0.25, from 10.1.0-M1 through 10.1.59, from 9.0.0.M1 through 9.0.121.
The following versions were EOS at the time the CVE was created but are known to be affected: from 8.5.0 through 8.5.100, from 7.0.43 through 7.0.109. Other unsupported versions may also be affected.
Users are recommended to upgrade to version 11.0.26, 10.1.60 or 9.0.122, which fix the issue.
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Analysis
by VulDB Data Team • 09/23/2026
A critical authentication bypass vulnerability has been identified in Apache Tomcat, specifically affecting its WebSocket implementation. This flaw allows an attacker to circumvent security constraints that are intended to protect specific WebSocket endpoints. The root cause lies in how the server processes and matches endpoint names against defined security roles during the handshake process. When a client initiates a connection to a protected WebSocket endpoint, the application server is supposed to verify if the authenticated user possesses the necessary permissions for that specific path or name. However, due to an inconsistency in the matching logic, it was possible to use alternate naming conventions or variations of the endpoint identifier to bypass these checks. This means that even if strict access controls were configured for a particular WebSocket route, an attacker could exploit this discrepancy to gain unauthorized access without valid credentials or with insufficient privileges.
The vulnerability impacts multiple major branches of Apache Tomcat, indicating a systemic issue within the core networking and security modules rather than an isolated bug in a single release cycle. Affected versions include all releases from 11.0.0-M1 through 11.0.25, as well as the long-term support branch covering 10.1.0-M1 to 10.1.59 and the legacy stable line spanning 9.0.0.M1 to 9.0.121. Additionally, older versions that have reached end-of-life status, specifically those from 8.5.0 through 8.5.100 and 7.0.43 through 7.0.109, are also known to be vulnerable. This widespread impact underscores the importance of maintaining up-to-date software environments, as even deprecated versions remain susceptible to exploitation in production systems that have not been decommissioned or patched via backports.
From a technical classification perspective, this vulnerability aligns with CWE-287, which describes Improper Authentication, and more specifically relates to authentication bypass mechanisms where alternative identifiers are used to evade security controls. In the context of the MITRE ATT&CK framework, this behavior is consistent with techniques involving credential access or privilege escalation through misconfigured application logic, often categorized under Initial Access or Persistence depending on how the compromised WebSocket connection is utilized post-exploitation. The ability to bypass authentication for real-time communication channels like WebSockets is particularly dangerous because these connections are typically long-lived and bidirectional, allowing attackers not only initial unauthorized entry but also sustained interaction with backend services that may handle sensitive data or execute privileged operations.
The operational impact of this vulnerability can be severe, depending on the application architecture and the sensitivity of the WebSocket endpoints involved. If a WebSocket endpoint is used for real-time notifications, chat functionalities, live updates, or administrative controls, an attacker could inject malicious messages, exfiltrate confidential information in real time, or manipulate stateful sessions without detection by standard authentication middleware. Since WebSockets often operate over HTTP upgrades, they may bypass traditional web application firewalls that are configured to inspect only standard request-response cycles, further increasing the risk of undetected intrusion. For applications relying on WebSocket connections for critical business logic, this flaw represents a significant security gap that could lead to data breaches or service disruption if left unaddressed.
To mitigate this vulnerability, organizations must ensure they upgrade their Apache Tomcat instances to patched versions immediately. The recommended fixed releases are 11.0.26, 10.1.60, and 9.0.122 for supported branches. For environments still running end-of-life versions such as the 8.5.x or 7.0.x series, immediate migration to a supported release is strongly advised, as backports may not be available from the Apache Software Foundation. In addition to upgrading, administrators should review their WebSocket security configurations and ensure that endpoint paths are strictly validated against defined roles using canonical names rather than relying on loose string matching where possible. Implementing additional network-level controls such as Web Application Firewalls with deep packet inspection capabilities for WebSocket traffic can provide a layer of defense in depth while the underlying software is being updated. Regular vulnerability scanning and patch management processes should be enforced to prevent similar issues from persisting in production environments.