CVE-2025-22940 is a critical security vulnerability affecting the Adtran 411 Optical Network Terminal (ONT) with firmware version L80.00.0011.M2. The vulnerability arises from incorrect access control mechanisms within the device's management interface, which allows an unauthenticated attacker to arbitrarily set the administrator password. This flaw effectively bypasses authentication controls (CWE-284: Improper Access Control), enabling attackers to gain full administrative privileges without any prior credentials or user interaction. The vulnerability has a CVSS v3.1 base score of 9.1, reflecting its high severity and ease of exploitation over the network (AV:N), with no privileges required (PR:N) and no user interaction needed (UI:N). Successful exploitation compromises the confidentiality and integrity of the device's configuration by allowing attackers to change the admin password, potentially leading to persistent unauthorized access, configuration manipulation, and further lateral attacks within the network. Although no known exploits have been reported in the wild yet, the vulnerability's nature and severity make it a significant risk for organizations deploying the affected Adtran ONT devices, especially in environments where these devices serve as critical network access points.

For European organizations, the impact of this vulnerability can be substantial, particularly for Internet Service Providers (ISPs), telecommunications companies, and enterprises relying on Adtran 411 ONT devices for broadband access or network edge connectivity. Unauthorized administrative access can lead to interception or manipulation of network traffic, disruption of services, and potential compromise of downstream systems connected through these ONTs. Confidential customer data and internal communications could be exposed or altered, undermining data privacy and regulatory compliance such as GDPR. Additionally, attackers could leverage compromised ONTs as footholds for broader network intrusion campaigns or to launch denial-of-service attacks against critical infrastructure. The lack of authentication requirements and the ability to exploit remotely increase the risk of widespread exploitation if the vulnerability is weaponized. This threat is particularly concerning for sectors with high availability and confidentiality requirements, including finance, healthcare, and government agencies within Europe.

Immediate mitigation steps include isolating affected Adtran 411 ONT devices from untrusted networks to limit exposure. Network segmentation should be enforced to restrict management interface access to trusted administrative hosts only. Organizations should monitor network traffic for unusual access attempts targeting ONT management interfaces. Since no official patches are currently available, applying vendor-recommended firmware updates as soon as they are released is critical. In the interim, consider implementing compensating controls such as deploying firewall rules to block external access to ONT management ports, enforcing strong network access controls, and using VPNs or secure management channels for administrative access. Regularly audit device configurations and access logs to detect unauthorized changes. Additionally, organizations should engage with Adtran support channels to obtain guidance and updates on patch availability and vulnerability remediation timelines.