CVE-2026-16931 in IBM
Summary
by MITRE • 08/12/2026
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 handling of zero-length TCP options.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 08/12/2026
This vulnerability affects IBM i operating systems version 7.6, 7.5, 7.4, and 7.3, presenting a remote denial of service risk through improper handling of zero-length TCP options. The flaw resides in the network stack's processing of Transmission Control Protocol options where the system fails to correctly manage TCP options with zero length fields. When a remote attacker sends specially crafted TCP packets containing zero-length options, the IBM i system may experience unexpected behavior leading to system instability and potential service disruption. This vulnerability aligns with CWE-129, which addresses improper handling of length parameters in network protocols, and represents a classic example of input validation failure in network services. The attack vector requires no authentication and can be executed remotely, making it particularly dangerous as it allows unauthenticated adversaries to disrupt system availability. The impact extends beyond simple service interruption as the system may crash or enter an unrecoverable state when processing malformed TCP options, potentially affecting critical business operations that rely on IBM i systems for enterprise applications and data processing. From a tactical perspective, this vulnerability maps to ATT&CK technique T1499.004 which covers network denial of service attacks targeting network infrastructure components. The flaw demonstrates poor error handling in the TCP option parsing mechanism where the system does not properly validate or sanitize TCP header options before processing them, leading to potential buffer overflows or state corruption within the network subsystem. Organizations running affected IBM i versions should consider immediate mitigation through firmware updates from IBM, network segmentation to limit exposure, and monitoring for unusual TCP traffic patterns that might indicate exploitation attempts. The vulnerability underscores the importance of robust input validation in network protocol implementations and highlights how seemingly benign protocol features can become attack vectors when not properly secured.
The technical implementation of this vulnerability stems from insufficient validation within the TCP option processing layer of IBM i's network stack. When the system encounters a TCP packet with zero-length options, it fails to properly validate these malformed headers before attempting to process them, potentially leading to memory corruption or unexpected execution paths. This improper handling creates a condition where valid network traffic could be used as a vector for denial of service attacks without requiring any privileged access or credentials. The vulnerability's classification under CWE-129 indicates that it involves inadequate validation of input parameters, specifically the length field in TCP options. From an operational standpoint, this weakness can be exploited by attackers using readily available network scanning tools to identify vulnerable systems and subsequently launch denial of service attacks. The attack could result in complete system unavailability, requiring manual intervention for recovery and potentially causing significant business disruption. Network administrators should implement traffic filtering rules to detect and block TCP packets with suspicious zero-length options while maintaining comprehensive logging of network activity to monitor for exploitation attempts. Organizations must also consider the broader implications of this vulnerability within their security posture, as it demonstrates potential weaknesses in protocol implementation that could affect other network services or applications running on the same infrastructure. The remediation process requires careful planning due to the critical nature of IBM i systems in enterprise environments and may involve coordinated updates to ensure business continuity while addressing the underlying TCP option handling flaw.