CVE-2025-59367 is an authentication bypass vulnerability categorized under CWE-288, discovered in the ASUS DSL-AC51 router series. The vulnerability allows remote attackers to bypass authentication mechanisms by exploiting an alternate path or channel within the device's firmware, enabling unauthorized access to the router's management interface or system functions. This bypass does not require any privileges, user interaction, or authentication, making it highly exploitable remotely over the network. The vulnerability affects firmware versions prior to 1.1.2.3_1010. The CVSS 4.0 base score is 9.3, reflecting its critical nature, with attack vector network (AV:N), low attack complexity (AC:L), no privileges required (PR:N), no user interaction (UI:N), and high impact on confidentiality, integrity, and availability (C:H, I:H, A:H). Although no exploits have been reported in the wild yet, the vulnerability poses a significant risk due to the potential for attackers to gain full control over affected routers, leading to interception or manipulation of network traffic, unauthorized configuration changes, or denial of service. ASUS has acknowledged the issue and is expected to release security updates; however, no patch links are currently provided. The vulnerability's presence in widely deployed consumer and small business routers increases the attack surface, especially in environments where these devices serve as gateways to corporate or home networks.

For European organizations, this vulnerability presents a severe risk to network security and operational continuity. Unauthorized access to DSL-AC51 routers can lead to interception of sensitive communications, manipulation of network configurations, and potential lateral movement within internal networks. Confidentiality is at risk as attackers could capture unencrypted data or redirect traffic to malicious endpoints. Integrity could be compromised through unauthorized configuration changes, potentially disabling security controls or enabling persistent backdoors. Availability may be affected if attackers disrupt router functionality or launch denial-of-service conditions. Given the critical CVSS rating and the lack of required authentication, exploitation could be automated and widespread, threatening small to medium enterprises and home office environments that rely on these routers. The impact extends to regulatory compliance, as breaches involving personal or sensitive data could trigger GDPR violations with significant penalties. The absence of known exploits in the wild currently provides a window for proactive mitigation, but the high severity demands urgent attention.

European organizations should immediately inventory their network infrastructure to identify any ASUS DSL-AC51 routers running vulnerable firmware versions. Until patches are available, restrict remote access to router management interfaces by disabling WAN-side management and limiting LAN-side access to trusted administrators only. Implement network segmentation to isolate vulnerable devices from critical systems and sensitive data. Monitor network traffic for unusual patterns indicative of unauthorized access attempts or configuration changes. Employ intrusion detection/prevention systems (IDS/IPS) with updated signatures to detect exploitation attempts. Once ASUS releases the security update, prioritize prompt firmware upgrades to version 1.1.2.3_1010 or later. Consider deploying compensating controls such as VPNs for remote management and multi-factor authentication where supported. Educate users and administrators about the risks and signs of compromise related to router vulnerabilities. Maintain regular backups of router configurations to facilitate recovery in case of compromise. Engage with ASUS support channels for official advisories and patch notifications.