CVE-2026-18511 is a stack-based buffer overflow vulnerability in IBM i versions 7.3, 7.4, 7.5, and 7.6 affecting the Native IBM i JSSE provider. The flaw arises from improper bounds checking during TLS session establishment, allowing a local authenticated attacker to overflow a fixed-length buffer. Successful exploitation could lead to arbitrary code execution on the system or cause the JVM process to crash. This vulnerability is categorized under CWE-787 (Out-of-bounds Write) and has a CVSS v3.1 score of 7.3 (high severity). No vendor advisory or patch information is currently available, and no known exploits are reported in the wild.

A local authenticated attacker can trigger a stack-based buffer overflow in the Native IBM i JSSE provider, potentially leading to arbitrary code execution or JVM process crashes. This could compromise system integrity or availability. The vulnerability affects confidentiality, integrity, and availability as indicated by the CVSS vector (C:L/I:L/A:L).

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until an official fix is available, limit local access to trusted users only and monitor for unusual JVM process behavior. No official remediation or temporary fix has been published by IBM at this time.