CVE-2026-93866 in Fireware OS
Summary
by MITRE • 10/27/2026
An integer overflow vulnerability in the WebSocket connection handling used by WatchGuard Fireware OS's Access Portal allows a remote, unauthenticated attacker to write beyond the bounds of a heap buffer by sending a specially crafted request while the Access Portal feature is enabled.
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Analysis
by VulDB Data Team • 10/27/2026
The identified vulnerability represents a critical security flaw within the Web Application Firewall and Remote Access components of WatchGuard Fireware OS, specifically affecting the implementation of the Access Portal's WebSocket connection handling mechanism. This integer overflow condition arises from an improper validation or arithmetic operation when processing incoming network packets destined for the Access Portal service. Because the vulnerability is located in the core logic that manages persistent connections via WebSockets, it allows a remote attacker to manipulate memory allocation sizes during the initialization of these sessions. The flaw enables the system to allocate less heap memory than required by the actual data payload size due to an integer wrap-around or truncation error. Consequently, when subsequent operations attempt to write the full-sized payload into this undersized buffer, they exceed the allocated boundaries, resulting in a heap-based buffer overflow.
From a technical perspective, this is classified as CWE-190: Integer Overflow or Wraparound leading directly to CWE-122: Heap-Based Buffer Overflow. The exploitation of this vulnerability does not require any form of authentication, making it particularly dangerous for devices exposed to the internet with the Access Portal feature enabled. An unauthenticated attacker can craft a malicious WebSocket frame containing specific header fields that trigger the integer miscalculation during memory allocation routines within the operating system's network stack or application layer processing logic. By sending this specially crafted request, the attacker forces the system to write data beyond the limits of the heap buffer into adjacent memory regions. This out-of-bounds write can corrupt internal data structures, overwrite function pointers, or alter control flow variables stored in nearby memory locations.
The operational impact of successfully exploiting this vulnerability is severe and multifaceted. The primary consequence is arbitrary code execution on the affected device with the privileges of the compromised process, which typically runs with high-level system access to manage firewall rules and network policies. This allows an attacker to gain full control over the WatchGuard appliance, potentially using it as a pivot point for lateral movement within the protected internal network. Furthermore, heap corruption can lead to application crashes or instability in the Access Portal service, resulting in a denial of service condition that disrupts legitimate remote access capabilities for authorized users. The ability to execute code remotely without authentication significantly lowers the barrier for exploitation, allowing automated scanning tools and opportunistic attackers to compromise vulnerable systems with minimal effort.
In terms of threat modeling, this vulnerability aligns with MITRE ATT&CK techniques related to initial access and privilege escalation via exploited remote services. Specifically, it falls under T1190: Exploit Public-Facing Application, as the Access Portal is a service designed for external connectivity. The exploitation path leverages memory corruption (T1203) to achieve code execution, which may subsequently be used to install backdoors or exfiltrate sensitive data stored on the firewall appliance. Given that firewalls often serve as critical choke points in network architecture, compromising one can lead to widespread visibility into and control over internal traffic flows.
Mitigation strategies must prioritize immediate patching of the WatchGuard Fireware OS to the latest version released by the vendor, which contains fixes for this integer overflow condition. Until patches are applied, administrators should consider disabling the Access Portal feature if it is not strictly required for business operations, thereby removing the attack surface associated with WebSocket handling in that context. Additionally, deploying network-level controls such as Intrusion Prevention System (IPS) signatures or Web Application Firewall rules can help detect and block malicious payloads attempting to exploit this vulnerability before they reach the vulnerable application logic. Regular security audits and monitoring of access portal logs for anomalous connection patterns are also recommended to identify potential exploitation attempts in real-time.