CVE-2026-17262 in IBM
Summary
by MITRE • 09/18/2026
IBM i 7.6, 7.5, 7.4, and 7.3 could allow a local attacker to cause a denial of service due to improper validation of FTP authentication commands.
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Analysis
by VulDB Data Team • 09/18/2026
The vulnerability identified in IBM i operating systems versions 7.3 through 7.6 represents a critical flaw within the File Transfer Protocol implementation that allows for localized exploitation resulting in system instability. This specific weakness stems from an insufficient validation mechanism applied to incoming FTP authentication sequences, which are fundamental components of establishing secure file transfer sessions. When a local attacker interacts with the affected service, they can craft maliciously formatted or excessively complex authentication commands designed to exploit parsing errors within the underlying protocol handler. The core technical failure lies in the system's inability to properly sanitize and validate these inputs before processing them against internal state machines responsible for managing user credentials and session contexts.
From a technical perspective, this flaw is classified under CWE-20 Improper Input Validation, as the application fails to verify that incoming data conforms to expected formats or length constraints prior to execution. The improper handling of authentication commands can lead to memory corruption, infinite loops within the FTP daemon process, or resource exhaustion conditions such as stack overflows. Because the vulnerability is triggered by local attackers, it implies that an individual with existing access privileges on the system but lacking administrative rights may leverage this flaw to disrupt service availability. This scenario highlights a classic privilege escalation vector where limited user capabilities are abused to impact broader system stability rather than gaining unauthorized elevated permissions directly through code execution.
The operational impact of exploiting this vulnerability is primarily centered around denial of service conditions affecting the FTP subsystem and potentially cascading into related services depending on how IBM i handles process isolation for network daemons. An attacker could repeatedly send malformed authentication packets, causing the FTP server to crash or become unresponsive to legitimate users. In enterprise environments where automated backup processes, data synchronization tasks, or legacy application integrations rely heavily on stable FTP connectivity, such disruptions can lead to significant workflow interruptions and potential data consistency issues if transfers are interrupted mid-stream without proper rollback mechanisms.
This vulnerability aligns with MITRE ATT&CK techniques related to Resource Hijacking and Service Disruption, specifically falling under the category of local privilege escalation via denial of service rather than direct control acquisition. While it does not immediately grant root access, its ability to degrade system reliability makes it a valuable tool for attackers seeking to mask other activities or create chaos during an intrusion attempt. The lack of robust input sanitization suggests that legacy code paths within older IBM i versions may still rely on outdated assumptions about network trust boundaries, even when those networks are considered internal and secure by default policies.
Mitigation strategies must focus on both immediate remediation and long-term architectural improvements. Organizations running affected versions should apply the latest security patches provided by IBM to address the validation logic flaws within the FTP service components. Until patching is feasible, administrators can implement network segmentation rules that restrict FTP access strictly to authorized IP ranges using firewall policies or host-based firewalls like iptables on compatible subsystems. Additionally enabling strict logging and monitoring for anomalous authentication failure rates can help detect attempted exploitation in real time. Long-term solutions involve migrating away from legacy FTP implementations toward more secure protocols such as SFTP or FTPS which enforce stronger encryption and validation standards, thereby reducing the attack surface associated with plaintext credential transmission and basic protocol parsing errors.