CVE-2026-18102: IBM i Buffer Overflow Vulnerability

CVE-2026-18102 Overview

CVE-2026-18102 is an integer underflow vulnerability affecting IBM i versions 7.6, 7.5, 7.4, and 7.3. The flaw occurs during bounds checking and allows a remote authenticated attacker to overwrite adjacent memory. Successful exploitation requires valid credentials on the target system and high attack complexity.

The vulnerability is classified under [CWE-122] (Heap-based Buffer Overflow) as a downstream consequence of the integer underflow. IBM has published guidance in an IBM Support Document.

Critical Impact
A remote authenticated attacker can trigger memory corruption in adjacent memory regions, potentially affecting the integrity of processes on affected IBM i systems.

Affected Products

IBM i 7.6
IBM i 7.5
IBM i 7.4
IBM i 7.3

Discovery Timeline

2026-08-19 - CVE-2026-18102 published to NVD
2026-08-20 - Last updated in NVD database

Technical Details for CVE-2026-18102

Vulnerability Analysis

The vulnerability stems from an integer underflow during bounds-checking logic in IBM i. When the affected routine calculates a size or offset value, the arithmetic wraps below zero and produces an unexpectedly large unsigned value. The bounds check then passes an operation that should have been rejected, leading to writes into memory adjacent to the intended buffer.

The outcome is memory corruption that affects integrity. The CVSS vector indicates the scope changes during exploitation, meaning the corruption crosses a security boundary and can influence resources beyond the vulnerable component. Confidentiality and availability are not directly impacted.

Exploitation requires the attacker to hold valid credentials on the IBM i system. The attack complexity is high, indicating that the attacker must satisfy specific conditions or win a race to reliably trigger the underflow. Refer to the IBM Support Document for vendor technical detail.

Root Cause

The root cause is an arithmetic operation on a signed or unsigned integer that underflows during size validation. The resulting value bypasses the intended length check. Subsequent memory operations use the malformed length and write past the allocated region, corrupting adjacent heap memory [CWE-122].

Attack Vector

The attack is network-based and requires authenticated access. An attacker sends crafted input to a network-exposed IBM i service that performs the flawed bounds computation. No user interaction is required. No verified public exploit code is available for this issue.

Detection Methods for CVE-2026-18102

Indicators of Compromise

Unexpected process termination or abend messages on IBM i subsystems handling network requests from authenticated users
Anomalous authenticated sessions initiating malformed protocol requests to IBM i services
Job log entries indicating memory access exceptions correlated with specific user profiles

Detection Strategies

Monitor IBM i audit journal (QAUDJRN) entries for authority failures, abnormal job endings, and integrity events tied to network services
Correlate authenticated session activity with subsequent service instability or restarts
Baseline normal request sizes for network-facing IBM i services and alert on outliers that could trigger arithmetic wrap conditions

Monitoring Recommendations

Forward IBM i audit and history logs to a centralized SIEM for correlation with authentication events
Track privileged user activity across IBM i partitions and alert on unusual command sequences
Review service restart frequency for network-exposed IBM i components after the disclosure date

How to Mitigate CVE-2026-18102

Immediate Actions Required

Apply the fixes referenced in the IBM Support Document for IBM i 7.6, 7.5, 7.4, and 7.3
Inventory all IBM i partitions in the environment and confirm current PTF levels
Restrict network access to IBM i services to trusted management networks only

Patch Information

IBM has published remediation guidance in the IBM Support Document. Administrators should install the PTFs identified by IBM for each affected release (7.3, 7.4, 7.5, 7.6). Verify PTF application using DSPPTF after installation.

Workarounds

Enforce least privilege on IBM i user profiles to reduce the population of accounts that can reach the vulnerable code path
Restrict network reachability of IBM i services with firewall rules and IBM i exit programs where feasible
Rotate credentials for accounts that may have been shared or exposed while patching is scheduled

bash

# Display installed PTFs on IBM i to verify remediation
DSPPTF LICPGM(5770SS1)