CVE-2025-8679 is a high-severity vulnerability affecting Extreme Networks' ExtremeGuest Essentials product versions prior to 25.5.0. The vulnerability stems from improper restriction of excessive authentication attempts (CWE-307) in the captive-portal functionality of the product. Specifically, under certain captive-portal SSID configurations, an unauthenticated attacker can perform a manual brute-force attack by repeatedly attempting to log in. Due to insufficient controls on the number of authentication attempts, the captive portal may incorrectly mark the attacker’s device as authenticated, granting unauthorized network access. Notably, the Client360 logs may show the client MAC address as the username, even though MAC authentication is not enabled, indicating a flaw in the authentication tracking mechanism. The CVSS 4.0 base score is 7.6, reflecting a high severity with attack vector being adjacent network (AV:A), high attack complexity (AC:H), no privileges or user interaction required, and high impact on confidentiality and integrity. This vulnerability allows an attacker within the wireless network range to bypass authentication controls and gain unauthorized access to the network, potentially exposing internal resources or sensitive data. No known exploits are currently reported in the wild, and no patches have been linked yet, indicating organizations should prioritize mitigation and monitoring until an official fix is released.

For European organizations deploying ExtremeGuest Essentials for guest Wi-Fi access, this vulnerability poses a significant risk. Unauthorized network access via the captive portal could lead to lateral movement within internal networks, data exfiltration, or use of the network for malicious activities such as launching attacks on other systems. Given that guest networks are often segmented but sometimes have access to critical resources or internet gateways, exploitation could undermine network segmentation strategies. This is particularly impactful for sectors with strict data protection regulations such as finance, healthcare, and government institutions in Europe, where unauthorized access could lead to compliance violations under GDPR and other frameworks. Additionally, the ability to bypass authentication without user interaction or privileges lowers the barrier for attackers, increasing the likelihood of exploitation in environments with dense wireless deployments such as corporate campuses, hotels, and conference centers. The lack of current known exploits provides a window for proactive defense, but the high severity score demands urgent attention to prevent potential breaches.

European organizations should immediately review their ExtremeGuest Essentials captive portal configurations, especially those using versions prior to 25.5.0. Specific mitigations include: 1) Restricting the number of authentication attempts per device or IP address to prevent brute-force attempts; 2) Enabling MAC authentication or other stronger device identification methods to complement captive portal authentication; 3) Monitoring Client360 logs for unusual patterns such as repeated login attempts or MAC addresses appearing as usernames; 4) Segmenting guest networks strictly to limit access to sensitive internal resources; 5) Applying network access control (NAC) solutions to enforce device compliance before granting network access; 6) Preparing to deploy the vendor’s patch once available and testing it in a controlled environment; 7) Educating network administrators on this vulnerability to ensure rapid detection and response; 8) Implementing wireless intrusion detection/prevention systems (WIDS/WIPS) to detect anomalous authentication behaviors. These steps go beyond generic advice by focusing on configuration hardening, enhanced monitoring, and network segmentation tailored to this specific vulnerability.