CVE-2026-18567 Overview
IBM Db2 Mirror for i versions 7.4, 7.5, and 7.6 contain a race condition vulnerability that allows a local attacker to obtain sensitive information. The flaw stems from a predictable Unix domain socket path created inside a world-writable directory. A local user can exploit the timing window between path creation and socket binding to intercept data intended for the legitimate service. The vulnerability is tracked as CWE-367: Time-of-Check Time-of-Use (TOCTOU) Race Condition.
Critical Impact
A local attacker with low privileges can win a race condition against Db2 Mirror for i and obtain confidential information passing through the Unix domain socket.
Affected Products
- IBM Db2 Mirror for i 7.4
- IBM Db2 Mirror for i 7.5
- IBM Db2 Mirror for i 7.6
Discovery Timeline
- 2026-09-04 - CVE-2026-18567 published to NVD
- 2026-09-08 - Last updated in NVD database
Technical Details for CVE-2026-18567
Vulnerability Analysis
IBM Db2 Mirror for i uses a Unix domain socket for inter-process communication. The socket path is predictable and resides in a world-writable directory. A local attacker who can enumerate or predict the path can create a competing file or socket at that location before the legitimate service binds to it. Successful exploitation leaks information handled through the socket. The attack impacts confidentiality only; integrity and availability remain unaffected according to the published CVSS vector.
Root Cause
The root cause is a Time-of-Check Time-of-Use (TOCTOU) flaw [CWE-367]. Db2 Mirror for i checks the state of the socket path and then acts on it in separate operations. Because the parent directory is world-writable, any local user can modify the path between those two steps. Placing the socket in a non-world-writable directory or using atomic creation semantics would eliminate the window of opportunity.
Attack Vector
Exploitation requires local access with low privileges and no user interaction. The attacker monitors the world-writable directory for socket creation activity by Db2 Mirror for i. When the service prepares to create the predictable socket, the attacker races to substitute a file, symbolic link, or attacker-controlled socket at the known path. Data written by the service or clients then flows to the attacker. The high attack complexity reflects the timing precision required to consistently win the race.
No public proof-of-concept code is available for this issue. Refer to the IBM Support Page for vendor technical details.
Detection Methods for CVE-2026-18567
Indicators of Compromise
- Unexpected files, symbolic links, or sockets appearing in the world-writable directory used by Db2 Mirror for i prior to service startup.
- Db2 Mirror for i error logs showing socket bind failures, permission errors, or unexpected owner mismatches.
- Local user processes with open file descriptors pointing at the Db2 Mirror socket path.
Detection Strategies
- Audit filesystem events on the world-writable directory to identify non-service processes creating entries matching the Db2 Mirror socket naming pattern.
- Correlate Db2 Mirror startup events with concurrent file-creation activity by non-privileged users.
- Review process accounting for local users invoking socket creation syscalls (bind, socket, symlink) targeting the affected directory.
Monitoring Recommendations
- Enable filesystem auditing on directories that host IBM i inter-process socket files.
- Alert on any local user session that opens or writes to Db2 Mirror socket paths outside the service account.
- Track privileged service restarts and correlate against user activity in the seconds preceding socket creation.
How to Mitigate CVE-2026-18567
Immediate Actions Required
- Apply the fix documented on the IBM Support Page for Db2 Mirror for i 7.4, 7.5, and 7.6.
- Restrict local login access to Db2 Mirror for i hosts to trusted administrators only.
- Review and tighten permissions on directories used by Db2 Mirror for socket communication.
Patch Information
IBM has published remediation guidance and fix availability on the IBM Support Page. Administrators should identify the appropriate PTF for each affected release (7.4, 7.5, 7.6) and apply it following IBM i change control procedures.
Workarounds
- Limit interactive and program-call access on the IBM i partition running Db2 Mirror to reduce the pool of potential local attackers.
- Monitor the world-writable directory hosting the socket path and alert on unexpected file creation until the PTF is applied.
- Where operationally acceptable, relocate or restrict access to the parent directory so only the Db2 Mirror service account can create entries.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
