Description

IBM i 7.6, 7.5, 7.4, and 7.3 could allow a local authenticated attacker to obtain unauthorized access to files due to a time-of-check time-of-use (TOCTOU) race condition.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "7.1",
  "pubDate": "2026-08-13T20:17:16.400Z",
  "pubdate": "2026-08-13T20:17:16.400Z",
  "executiveSummary": "A time-of-check time-of-use (TOCTOU) race condition vulnerability has been identified in IBM i versions 7.6, 7.5, 7.4, and 7.3. This vulnerability allows a local authenticated attacker to obtain unauthorized access to sensitive files on the underlying system. The flaw stems from a synchronization discrepancy between the validation of access permissions and the subsequent execution of file operations. If successfully exploited, the integrity and confidentiality of critical system data may be compromised. The attacker must possess local authentication and specific execution capabilities on the target system to initiate the race condition. Risk implications involve unauthorized data disclosure and potential escalation of privileges through manipulation of file states during execution intervals. Remediation requires applying official vendor patches or configuration updates as provided by IBM to resolve synchronization flaws.",
  "technicalDetails": "The vulnerability is rooted in a classical time-of-check time-of-use (TOCTOU) race condition within the file management and security validation subsystems of IBM i. The affected components fail to properly serialize or atomically execute security state verification and the actual file access operation. Specifically, when a process requests access to a file resource, the operating system kernel performs a security check (time-of-check) to validate whether the authenticated subject holds the necessary permissions for the requested object. However, a measurable temporal window exists between this authorization check and the moment the file handle is actually utilized or acted upon (time-of-use). During this execution window, a locally authenticated attacker can manipulate the target file system path—such as swapping a benign file with a symlink or substituting a resource—such that the kernel operates on a restricted file using the previously validated, elevated permission context or bypasses access controls entirely. Exploitation requires the attacker to have local authenticated access to the IBM i environment and the ability to execute concurrent processes or threads optimized to repeatedly hit the precise temporal window of the race condition. The attack flow involves initiating asynchronous threads that repeatedly trigger the vulnerable file operation while concurrently modifying the symbolic links or directory structures targeted by the system call. If the timing aligns successfully, the kernel evaluates permissions against one object state but performs the I/O operation on another, resulting in unauthorized file access, potential information disclosure, or corruption of protected system resources. Network exposure is not a prerequisite, as the attack vector is strictly local. Privilege requirements dictate that the attacker must already be authenticated locally, though the ultimate post-exploitation impact depends on the privilege context of the targeted process or the sensitivity of the accessed files."
}