CVE-2025-11561 is a vulnerability discovered in the integration between Active Directory (AD) and the System Security Services Daemon (SSSD) on Linux systems, specifically Red Hat Enterprise Linux 10. The flaw involves the Kerberos local authentication plugin (sssd_krb5_localauth_plugin), which is enabled by default. This plugin is designed to authenticate users locally using Kerberos tickets. However, the system allows a fallback to the an2ln plugin under certain conditions. This fallback mechanism can be exploited by an attacker who has the ability to modify specific AD attributes such as userPrincipalName or samAccountName. By altering these attributes, the attacker can impersonate privileged users within the domain-joined Linux environment. This impersonation can lead to unauthorized access and privilege escalation, compromising the confidentiality, integrity, and availability of the affected systems. The vulnerability requires the attacker to have some level of permission to modify AD attributes but does not require user interaction, making it easier to exploit remotely. The CVSS v3.1 score of 8.8 reflects the high impact and relatively low complexity of exploitation. Although no exploits are currently known in the wild, the vulnerability poses a significant risk to organizations relying on AD-SSSD integration for authentication on Linux hosts. The issue highlights the risks of fallback authentication mechanisms and the importance of strict AD attribute permission controls.

For European organizations, this vulnerability poses a serious threat to the security of domain-joined Linux systems, particularly those running Red Hat Enterprise Linux 10. The ability for an attacker to impersonate privileged users can lead to unauthorized access to sensitive data, disruption of critical services, and potential lateral movement within corporate networks. Organizations in sectors such as finance, government, healthcare, and critical infrastructure, which often rely on Active Directory for centralized authentication and use Linux servers, are at heightened risk. The compromise of privileged accounts can result in data breaches, regulatory non-compliance (e.g., GDPR), and significant operational downtime. Given the widespread use of Red Hat Enterprise Linux in European enterprises and public sector environments, the vulnerability could have broad impact if exploited. The lack of known exploits in the wild currently provides a window for proactive mitigation, but the high severity score underscores the urgency of addressing the issue.

1. Immediately apply any available patches or updates from Red Hat addressing CVE-2025-11561 once released. 2. Until patches are available, disable the fallback to the an2ln plugin in the SSSD configuration to prevent exploitation of the fallback mechanism. 3. Restrict permissions in Active Directory to tightly control which users or groups can modify sensitive attributes such as userPrincipalName and samAccountName. 4. Implement monitoring and alerting on changes to these AD attributes to detect potential malicious modifications early. 5. Conduct regular audits of AD permissions and SSSD configurations to ensure compliance with least privilege principles. 6. Employ network segmentation and access controls to limit the exposure of domain-joined Linux hosts to untrusted networks. 7. Educate administrators about the risks of fallback authentication mechanisms and the importance of secure integration between AD and Linux authentication services. 8. Consider deploying multi-factor authentication (MFA) for privileged accounts to add an additional layer of security.