CVE-2026-17255 in IBM
Summary
by MITRE • 09/04/2026
IBM i 7.6, 7.5, 7.4, and 7.3 could allow a remote attacker to cause a denial of service due to improper validation of the prefix length in ICMPv6 Router Advertisements.
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Analysis
by VulDB Data Team • 09/04/2026
The vulnerability identified affects IBM i operating system versions including releases 7.6, 7.5, 7.4, and 7.3. This security flaw resides within the implementation of Internet Control Message Protocol version six handling mechanisms, specifically concerning the processing of Router Advertisement messages. These messages are a critical component of the Neighbor Discovery Protocol used in IPv6 networks to allow hosts to discover routers on their local link segment. The core technical deficiency involves an improper validation mechanism for the prefix length field contained within these ICMPv6 Router Advertisements. When the system receives such packets, it fails to adequately verify that the specified prefix length falls within acceptable bounds or is logically consistent with other parameters in the message structure. This lack of rigorous input sanitization allows a remote attacker to craft maliciously formatted packets containing invalid or extreme values for this field.
The operational impact of this vulnerability centers on service disruption rather than unauthorized access or data exfiltration. Because the system does not properly validate the prefix length, processing these malformed messages can lead to resource exhaustion, memory corruption, or internal logic errors that cause network stack components to fail. Consequently, an unauthenticated remote attacker located anywhere in the network path could exploit this flaw by sending specially crafted ICMPv6 Router Advertisement packets. The successful exploitation of this issue results in a denial of service condition where affected systems may become unresponsive, crash, or require manual intervention and rebooting to restore normal functionality. This degradation of availability directly impacts business continuity and operational stability for organizations relying on these IBM i platforms for critical workloads.
From a classification perspective, this vulnerability aligns with Common Weakness Enumeration identifier CWE-20 which denotes Improper Input Validation. The failure to check the validity of data received from an external source before processing it is a fundamental security anti-pattern that leads to various downstream issues including crashes and instability. In terms of offensive cybersecurity frameworks, this exploit scenario maps to MITRE ATT&CK technique T1498 Network Denial of Service which covers actions intended to disrupt or impair the availability of targeted resources. The specific vector involves abusing protocol-level features for ICMPv6 traffic to trigger system failures without requiring authentication credentials, making it a significant risk in environments where IPv6 is enabled and active.
Mitigation strategies must address both immediate remediation and long-term architectural resilience. IBM has released patches that correct the validation logic within the network stack to ensure prefix lengths are checked against defined limits before processing proceeds. Organizations should prioritize applying these security updates to all affected systems as soon as possible. In addition to patching, defensive measures such as implementing ingress filtering on edge routers can help mitigate this risk by dropping malformed ICMPv6 packets from external sources that do not adhere to RFC standards for prefix length values. Network monitoring tools should also be configured to detect anomalous spikes in ICMPv6 Router Advertisement traffic which may indicate an ongoing exploitation attempt allowing security teams to respond proactively before significant service disruption occurs.