CVE-2026-16967 in IBM
Summary
by MITRE • 08/13/2026
IBM i 7.6, 7.5, 7.4, and 7.3 could allow a remote authenticated attacker to gain unauthorized access to system objects due to a time-of-check to time-of-use (TOCTOU) race condition involving symbolic links.
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Analysis
by VulDB Data Team • 08/13/2026
This vulnerability represents a critical time-of-check to time-of-use race condition that affects IBM i operating systems version 7.6, 7.5, 7.4, and 7.3. The flaw occurs when the system performs a permission check on a symbolic link and subsequently accesses the target object, creating an opportunity for malicious actors to exploit the temporal gap between these operations. Attackers can manipulate the symbolic link target between the time of permission validation and actual access, potentially gaining unauthorized access to system objects they would not normally be able to reach.
The technical implementation of this vulnerability stems from improper handling of symbolic link resolution within the IBM i file system security model. When an authenticated user attempts to access a symbolic link, the system initially validates permissions against the link itself before resolving it to its target object. If an attacker can modify or replace the symbolic link target during this brief window, they may redirect access to privileged system objects that would otherwise be protected by appropriate access controls. This race condition specifically impacts the privilege escalation capabilities of authenticated attackers who have legitimate access to the system but seek to bypass normal security boundaries.
From an operational impact perspective, this vulnerability creates a significant security risk for organizations relying on IBM i systems, as it allows for unauthorized access to sensitive system objects without requiring additional exploitation techniques. The authenticated nature of the attack means that threat actors need only valid user credentials to attempt exploitation, making the attack surface more accessible compared to privilege escalation methods requiring additional initial compromise. Organizations may experience unauthorized data access, potential system integrity compromise, and possible lateral movement opportunities if attackers successfully leverage this vulnerability to access critical system resources.
The underlying cause of this issue aligns with CWE-367 Time-of-Check to Time-of-Use Race Condition, which specifically addresses security flaws where an attacker can manipulate the state of a resource between a permission check and actual use. From an ATT&CK framework perspective, this vulnerability maps to privilege escalation techniques and potentially to lateral movement if attackers can access system objects with elevated privileges. The vulnerability's remote nature means that attackers do not require physical access to the system, and the authenticated requirement implies that initial compromise could occur through other vectors such as credential theft or social engineering.
Mitigation strategies should focus on immediate patch application from IBM to address the specific race condition in symbolic link handling. Organizations should implement monitoring for suspicious symbolic link modifications and access patterns that might indicate exploitation attempts. Network segmentation and least-privilege access controls can help limit the potential impact of successful exploitation, while regular security audits should verify proper symbolic link usage and identify any potentially vulnerable configurations. Additionally, system administrators should consider implementing automated tools to detect and prevent unauthorized symbolic link manipulations, particularly in directories where users might have write permissions but should not be able to create or modify links that could redirect access to protected resources.