CVE-2026-104033 in sssd
Summary
by MITRE • 10/06/2026
A flaw was found in SSSD. When configured to enforce account expiration using LDAP (Lightweight Directory Access Protocol) shadow attributes, SSSD fails to treat an expiration value of zero as an expired account. A user with valid credentials for an expired account can exploit this flaw to bypass access controls and authenticate to the system. This allows unauthorized access to persist after the account was intended to be deactivated.
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Analysis
by VulDB Data Team • 10/06/2026
The System Security Services Daemon, commonly known as SSSD, serves as a critical component in Linux-based environments by providing identity management and authentication services for distributed systems. It acts as an intermediary between local system security modules and remote directory servers such as LDAP or Active Directory. In configurations where account lifecycle management is delegated to the directory server via shadow attributes, SSSD relies on these external values to determine user eligibility for login. The identified vulnerability represents a logical flaw in how SSSD interprets specific expiration timestamps within this protocol-based authentication flow. Specifically, when an administrator configures LDAP shadow attributes to enforce strict account expiration policies, SSSD fails to correctly process the value zero as a definitive indicator of an expired status. This misinterpretation creates a gap between the intended security policy and its actual enforcement mechanism at the daemon level.
From a technical perspective, this issue stems from how the software evaluates boolean conditions related to time-based access controls. In many directory schemas, including those used in LDAP environments, specific numeric values carry distinct semantic meanings regarding account state. A value of zero for an expiration date is often standardized as a representation of immediate or indefinite expiry depending on the schema version and implementation context. However, SSSD’s logic appears to treat this zero value inconsistently with other non-zero timestamps that clearly indicate past dates. Consequently, when a user attempts to authenticate using credentials associated with such an account, the daemon does not trigger the expected denial response. Instead, it proceeds through the authentication handshake as if the account were still active and within its valid time window. This behavior effectively nullifies the administrative intent to revoke access based on temporal constraints defined in the directory service.
The operational impact of this vulnerability is significant for organizations relying on automated identity lifecycle management. In enterprise environments, accounts are frequently deactivated or expired automatically upon employee termination, role changes, or project completion. These actions are typically executed by updating shadow attributes in LDAP rather than manually disabling local user entries. If SSSD fails to recognize these expiration markers, former employees or decommissioned service accounts retain the ability to log into systems they should no longer access. This persistence of unauthorized access creates a substantial security risk, as it allows attackers who have compromised credentials for such accounts to maintain footholds within the network long after detection and remediation efforts were expected to take effect. It undermines the principle of least privilege by allowing continued interaction with system resources without proper authorization.
This flaw aligns closely with CWE-284, which describes Improper Access Control, specifically relating to failure to enforce access restrictions in a timely manner or under specific conditions. Furthermore, from an adversary perspective, this vulnerability facilitates techniques categorized under MITRE ATT&CK T1078, Valid Accounts. Attackers often seek valid credentials for legitimate users to blend in with normal traffic and avoid detection by security monitoring tools. By exploiting the failure of SSSD to enforce expiration policies, adversaries can leverage these stale accounts to move laterally across networks or escalate privileges without triggering alerts associated with invalid login attempts. The persistence of access through expired accounts complicates incident response efforts because standard auditing logs may not immediately flag the activity as anomalous if the credentials themselves are syntactically valid and currently active in the directory’s view, despite being logically expired according to policy.
Mitigating this vulnerability requires a multi-layered approach involving both software updates and configuration hardening. The primary remediation is to apply vendor-provided patches that correct the logical evaluation of expiration values within SSSD codebases. Administrators should ensure their systems are updated to versions where this specific handling of LDAP shadow attributes has been rectified. In addition to patching, organizations should implement compensating controls such as regular audits of user accounts against directory records to identify any discrepancies between local authentication states and central identity management policies. Utilizing network segmentation can also limit the blast radius if an expired account is compromised by restricting lateral movement opportunities. Furthermore, enabling comprehensive logging for authentication events allows security operations centers to detect patterns indicative of access using potentially stale credentials, providing a secondary line of defense against exploitation of this logical flaw until permanent fixes are deployed across all affected endpoints.