i: Time-of-check Time-of-use (TOCTOU) Race Condition
CVE-2026-16967 is a high-severity time-of-check time-of-use (TOCTOU) race condition vulnerability in i from IBM, with a CVSS 3.1 base score of 7.5 out of 10. It can be exploited remotely over the network by an attacker with a low-privileged account, without any action from a user. Affected i versions: 7.6; 7.5; 7.4, and others listed below. The record does not name a fixed version, so check the vendor advisory. There is no confirmed exploitation so far. EPSS estimates a 0.35% chance of exploitation within 30 days, which is low compared with other CVEs.
High severity with no evidence of exploitation so far.
What to do
- Check which version of i you run against the affected versions below, and install the vendor's latest release.
- Read the advisory on ibm.com for workarounds and exact fixed builds.
Affected products and versions
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- HighSuccess depends on conditions outside the attacker's control.
- Privileges required
- LowA basic user account is enough.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- HighData or code can be modified at will.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 3.1 | 8.5 | High | CNA (us.ibm.com) |
| CVSS 3.1 | 7.5 | High | NVD |
Official description
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.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Time-of-check Time-of-use (TOCTOU) Race Condition
The product checks the state of a resource before using that resource, but the resource's state can change between the check and the use in a way that invalidates the results of the check.
How developers prevent this class of flaw
- The most basic advice for TOCTOU vulnerabilities is to not perform a check before the use. This does not resolve the underlying issue of the execution of a function on a resource whose state and identity cannot be assured, but it does help to limit the false sense of security given by the check.
- When the file being altered is owned by the current user and group, set the effective gid and uid to that of the current user and group when executing this statement.
- Limit the interleaving of operations on files from multiple processes.
More Time-of-check Time-of-use (TOCTOU) Race Condition vulnerabilities (CWE-367)
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Advisories
Other vulnerabilities in i
- 7.8 High severity
- 9.9 Critical severity
- 8.1 High severity
- 7.8 High severity
- 9.8 Critical severity
- 7.5 High severity
Recent Time-of-check Time-of-use (TOCTOU) Race Condition vulnerabilities
- 9.9 Critical severity
- 7.8 High severity
- 8.8 High severity
- 7.4 High severity
- 8.1 High severity
- 8.1 High severity
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