CVE-2026-17491 in IBM
Summary
by MITRE • 10/16/2026
IBM i 7.3, 7.4, 7.5, and 7.6 is could allow a remote authenticated attacker to bypass security restrictions due to improper enforcement of the ChrootDirectory configuration directive.
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Analysis
by VulDB Data Team • 10/16/2026
The vulnerability identified in IBM i operating system versions 7.3 through 7.6 represents a critical failure in access control mechanisms within the Secure Shell subsystem, specifically concerning the implementation of directory isolation for user accounts. This flaw stems from an improper enforcement of the ChrootDirectory configuration directive, which is designed to restrict users to their home directories after authentication. The core technical issue lies in how the system processes path traversal sequences and symbolic links during session initialization or subsequent file operations within the restricted environment. Instead of strictly confining the user process to the designated chroot jail, certain conditions allow an authenticated attacker to escape this boundary by exploiting inconsistencies in path resolution logic. This misconfiguration effectively nullifies one of the primary defense-in-depth layers intended to limit lateral movement and data exposure for compromised accounts.
From a technical perspective, the vulnerability allows remote authenticated attackers to bypass security restrictions that are meant to contain user activities within specific filesystem boundaries. When an attacker successfully authenticates using valid credentials, they expect their access to be limited by the chroot environment. However, due to the improper enforcement of this directive, it is possible for malicious actors to navigate outside the intended directory structure. This escape capability can be achieved through various methods depending on the specific implementation details, such as manipulating relative path references or exploiting race conditions in file system operations that precede the final confinement check. The result is a state where the attacker gains access to files and directories that should remain inaccessible under normal operational policies, effectively elevating their privileges from a restricted user context to one with broader filesystem visibility.
The operational impact of this vulnerability is significant for organizations relying on IBM i systems for secure data hosting or multi-tenant environments. An authenticated attacker who exploits this flaw can read sensitive configuration files, access proprietary source code, exfiltrate customer data, or modify system settings that were previously protected by the chroot restriction. This breach of isolation undermines trust in the security model and can lead to further exploitation vectors, such as privilege escalation if additional vulnerabilities exist within the accessible areas. Furthermore, it compromises audit integrity because actions taken outside the expected directory may not be logged with appropriate context or restrictions, making forensic analysis more difficult. The ability to bypass these controls means that even strong authentication mechanisms are insufficient to guarantee data confidentiality and integrity without addressing this underlying architectural flaw.
This vulnerability aligns closely with Common Weakness Enumeration category CWE-284, which describes Improper Access Control, specifically relating to the failure to enforce restrictions on resources accessible by authenticated users. It also maps to MITRE ATT&CK techniques related to Lateral Movement and Discovery, as an attacker uses this escape to explore restricted areas of the system for further exploitation opportunities. The lack of proper enforcement in chroot implementations is a known class of issues that requires rigorous testing during development and deployment phases to ensure that path canonicalization occurs correctly before access checks are applied.
To mitigate this risk, organizations running IBM i versions 7.3 through 7.6 must apply the latest security patches provided by IBM as soon as possible. These updates typically include corrected code paths for handling chroot directory configurations and enhanced validation logic to prevent escape sequences from being processed incorrectly. In addition to patching, administrators should review their SSH daemon configuration files to ensure that ChrootDirectory directives are applied consistently across all user accounts where isolation is required. Implementing additional network-level controls such as firewalls can help limit exposure by restricting SSH access to trusted IP addresses only. Regular auditing of system logs for unusual file access patterns outside expected directories can also aid in early detection of exploitation attempts while waiting for full remediation deployment.