Description

IBM i 7.6, 7.5, 7.4, and 7.3 could allow a remote authenticated attacker to corrupt memory due to an integer underflow.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "6.3",
  "pubDate": "2026-09-04T17:16:56.283Z",
  "pubdate": "2026-09-04T17:16:56.283Z",
  "executiveSummary": "This vulnerability involves an integer underflow flaw within the memory management mechanisms of IBM i, affecting versions 7.3, 7.4, 7.5, and 7.6. An integer underflow occurs when an arithmetic operation results in a value smaller than the minimum representable integer, often leading to unexpected memory allocation sizes or pointer arithmetic errors.\nThe vulnerability permits a remote authenticated attacker to induce memory corruption, which can compromise the integrity, availability, and potentially the confidentiality of the affected system. Exploitation requires the attacker to possess authenticated access to the target environment. Successful exploitation could lead to arbitrary code execution, system crashes (Denial of Service), or privilege escalation, depending on the specific memory regions impacted by the corruption.\nGiven the nature of memory corruption vulnerabilities, this flaw represents a significant risk to the IBM i platform, necessitating prompt attention. Organizations should prioritize assessing their current exposure and implementing recommended security updates provided by IBM to remediate this vulnerability.",
  "technicalDetails": "The root cause of this vulnerability is an integer underflow condition within a critical component of the IBM i operating system, impacting versions 7.3, 7.4, 7.5, and 7.6. An integer underflow typically arises when the result of a subtraction operation on an unsigned integer variable drops below zero, causing it to wrap around to a very large positive value due to modular arithmetic behavior in computer architecture. This incorrect, large value is subsequently used in downstream operations, such as memory allocation or buffer bounds checking.\nIn the context of this vulnerability, the flaw likely manifests during the processing of specially crafted input or requests provided by a remote authenticated attacker. When the underlying system component performs arithmetic on user-controlled inputs that influence memory sizing, the underflow produces a severely miscalculated value. If this value is utilized to determine the size of a memory buffer allocation, the system may allocate a significantly smaller buffer than required, or conversely, bypass boundary checks entirely.\nThe exploitation flow begins with the authenticated attacker identifying an input vector that influences the vulnerable integer arithmetic. By carefully crafting the input values, the attacker forces the integer underflow to occur. Following the underflow, the system performs an operation using the incorrect value—for instance, copying data into a heap-allocated buffer. Because the buffer size was improperly determined due to the underflow, the copy operation results in a buffer overflow or heap corruption. This corruption can overwrite critical system structures, function pointers, or data objects residing in adjacent memory segments.\nPost-exploitation, the attacker may gain the ability to redirect the program control flow by overwriting return addresses or function pointers. This enables the execution of arbitrary, attacker-supplied payloads with the privileges of the affected component, which often run with high-level system permissions. Alternatively, the attacker may deliberately trigger a crash of a core operating system service, resulting in a Denial of Service condition that impacts the stability and availability of the IBM i system. The requirement for prior authentication acts as a barrier, limiting the attack surface to malicious insiders or attackers who have successfully compromised valid user credentials."
}