CVE-2019-9579 in NexentaStor
Summary
by MITRE • 12/26/2022
An issue was discovered in Illumos in Nexenta NexentaStor 4.0.5 and 5.1.2, and other products. The SMB server allows an attacker to have unintended access, e.g., an attacker with WRITE_XATTR can change permissions. This occurs because of a combination of three factors: ZFS extended attributes are used to implement NT named streams, the SMB protocol requires implementations to have open handle semantics similar to those of NTFS, and the SMB server passes along certain attribute requests to the underlying object (i.e., they are not considered to be requests that pertain to the named stream).
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Analysis
by VulDB Data Team • 11/27/2024
The vulnerability described in CVE-2019-9579 represents a critical access control flaw within the SMB server implementation of Illumos-based systems, specifically affecting NexentaStor 4.0.5 and 5.1.2 deployments. This issue stems from a fundamental design conflict between ZFS extended attributes and SMB protocol requirements for handle semantics, creating an unintended privilege escalation pathway that allows attackers with minimal permissions to manipulate system security controls. The vulnerability manifests when an attacker possessing WRITE_XATTR permissions can alter file permissions, effectively bypassing the normal access control mechanisms that should protect system resources from unauthorized modification.
The technical root cause of this vulnerability lies in the improper handling of extended attributes within the ZFS filesystem when interfacing with SMB protocol implementations. ZFS extended attributes are utilized to implement NT named streams, which are essential for maintaining compatibility with Windows file system semantics. However, the SMB server implementation fails to properly distinguish between operations targeting the primary file object versus those intended for named streams. This lack of proper separation leads to attribute requests being passed directly to the underlying ZFS object without appropriate permission checks or context awareness, creating a scenario where stream-related operations can inadvertently affect the parent file's metadata and permissions.
The operational impact of this vulnerability extends beyond simple permission modification, as it fundamentally undermines the security model of the file system by allowing attackers to manipulate access controls through seemingly benign extended attribute operations. An attacker with WRITE_XATTR privileges can exploit this flaw to elevate their effective permissions, potentially gaining access to resources that should remain restricted. This vulnerability directly relates to CWE-284, which addresses improper access control, and demonstrates how improper handling of file system metadata can create security boundaries that are easily circumvented. The flaw essentially creates a backdoor through which unauthorized modifications can be made to file permissions, compromising the integrity of the access control system.
The security implications of this vulnerability align with ATT&CK technique T1078.002, which covers legitimate credentials usage, as attackers can leverage existing permissions to gain elevated access through the flawed attribute handling mechanism. Organizations running affected systems face significant risks including unauthorized data access, privilege escalation, and potential lateral movement within their network infrastructure. The vulnerability is particularly concerning because it operates at the filesystem level, making it difficult to detect through traditional network monitoring approaches. Mitigation strategies should focus on implementing proper attribute request filtering, establishing clear boundaries between stream operations and primary file operations, and ensuring that permission checks are appropriately enforced at each level of the file system abstraction. Additionally, system administrators should consider disabling unnecessary extended attribute functionality when not required for specific use cases, and implement monitoring solutions that can detect anomalous permission modification patterns that may indicate exploitation attempts.