CVE-2026-104036 in Red Hat
Summary
by MITRE • 10/06/2026
A flaw was found in SSSD's NFS idmap plugin. When retrieving cached user or group names, the plugin detects if an entry exceeds the destination buffer size but fails to abort before copying data. A local attacker can trigger this vulnerability by requesting identity lookups that resolve to oversized cached entries, resulting in an out-of-bounds write. This flaw primarily leads to a Denial of Service (DoS) by crashing the identity mapping service, and may also corrupt adjacent process memory.
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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 environments for managing authentication and authorization across diverse directory services such as Active Directory, LDAP, and Kerberos. Within this architecture, the NFS idmap plugin plays a specific role in mapping user and group identities to numeric identifiers that are compatible with Network File System protocols. A significant vulnerability has been identified within this plugin concerning its handling of cached identity data during retrieval operations. The core technical flaw lies in the buffer management logic used when resolving cached entries for users or groups. Specifically, while the code correctly detects if an incoming entry exceeds the size of the destination buffer allocated to hold it, the execution flow fails to abort the operation before proceeding with the copy action. This logical error results in a classic out-of-bounds write condition where data is written beyond the limits of the intended memory region.
From a technical perspective, this vulnerability aligns closely with CWE-787, which describes an out-of-bounds write that occurs when a pointer writes to a memory location beyond the end of an allocated buffer. The attacker's role in exploiting this flaw is strictly local and requires authentication or access privileges sufficient to trigger identity lookups against the SSSD service. By crafting requests for identities that resolve to oversized cached entries, a malicious actor can force the plugin into executing the flawed copy routine. Because the check for buffer size limits does not halt execution prior to the memory write operation, the excess data spills over into adjacent memory spaces. This behavior is characteristic of CWE-120, which covers buffer copies without checking for overflow boundaries, although in this specific instance, the detection exists but is functionally bypassed due to incorrect control flow sequencing.
The operational impact of this vulnerability is primarily centered on service availability and system stability rather than immediate remote code execution or privilege escalation under default configurations. The most direct consequence is a Denial of Service caused by the crash of the identity mapping service within SSSD. When the out-of-bounds write corrupts critical memory structures, it triggers segmentation faults or other fatal errors that terminate the affected process. This disruption can prevent legitimate users from authenticating or accessing network resources until the service is restarted and caches are cleared. Furthermore, if the adjacent memory contains sensitive data or control flow pointers belonging to neighboring processes or internal SSSD state variables, there is a potential for more severe consequences such as information disclosure or arbitrary code execution, although these outcomes depend heavily on specific system configurations and memory layout conditions not guaranteed by the vulnerability itself.
In terms of threat modeling, this flaw can be mapped to MITRE ATT&CK techniques related to resource hijacking and service disruption. Specifically, it relates to T1499 Endpoint Denial of Service, where an attacker degrades or disrupts the availability of endpoint services. While not a network-based attack vector, its local nature means it falls under lateral movement or initial access scenarios if combined with other vulnerabilities that allow code execution on the host. The lack of bounds checking enforcement before memory operations highlights a common class of defects in systems programming where error handling paths are incomplete.
Mitigation strategies for this vulnerability focus primarily on software updates and configuration hardening. Administrators should apply vendor-provided patches that correct the control flow logic to ensure the copy operation is aborted when buffer size limits are exceeded. Until patching is feasible, limiting local access privileges to systems running vulnerable versions of SSSD can reduce the attack surface. Additionally, enabling robust logging for identity resolution failures may help in detecting attempted exploitation activities. Regular auditing of system logs for unexpected service restarts or crashes associated with sssd-nfs-idmapd processes can serve as an early warning indicator for potential abuse of this flaw. Maintaining up-to-date security patches remains the most effective defense against such memory corruption vulnerabilities that stem from logical errors in buffer handling routines.