CVE-2026-18869 in IBM
Summary
by MITRE • 09/18/2026
IBM i 7.6, 7.5, 7.4, and 7.3 could allow a remote authenticated attacker to bypass security restrictions and access internal network services due to improper validation of FTP PORT and EPRT commands.
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Analysis
by VulDB Data Team • 09/18/2026
The vulnerability identified in IBM i versions 7.6, 7.5, 7.4, and 7.3 represents a critical flaw within the File Transfer Protocol implementation that allows for security restriction bypasses through command injection techniques. This issue specifically targets the handling of PORT and EPRT commands during active FTP sessions. In standard FTP operations, these commands are used by the client to instruct the server on which IP address and port number to connect back to in order to establish a data connection. The core technical flaw lies in the insufficient validation of the parameters provided within these commands. An attacker who has successfully authenticated as a legitimate user can manipulate these fields to include malicious payloads or redirect connections to internal network addresses that are otherwise inaccessible from external networks. This improper validation mechanism effectively allows an authenticated actor to exploit the trust relationship between the FTP service and the underlying operating system, leading to unauthorized access to sensitive internal resources.
From a technical perspective, this vulnerability is classified under CWE-20 Improper Input Validation within the Common Weakness Enumeration framework. The root cause stems from the application's failure to rigorously sanitize or validate user-supplied input before processing it for network connection establishment. By accepting arbitrary IP addresses and port numbers without adequate checks against allowed ranges or internal address spaces, the system inadvertently facilitates a form of server-side request forgery specific to FTP protocols. This flaw enables an attacker to pivot from their initial foothold on the external-facing service to deeper layers of the corporate network infrastructure. The ability to force the FTP daemon to initiate connections to arbitrary destinations effectively turns the vulnerable service into a proxy or tunneling mechanism, allowing traffic that should be blocked by perimeter firewalls to traverse through the trusted internal interface of the IBM i system.
The operational impact of this vulnerability is significant for organizations relying on these versions of IBM i for file transfer operations. An authenticated remote attacker can leverage this flaw to map out internal network topologies, access restricted database services, or interact with other backend applications that are not exposed directly to the internet but are reachable from within the local subnet. This capability undermines the principle of least privilege and compromises the integrity of the network segmentation strategy. Furthermore, because the attack requires authentication, it targets users who have already passed initial security controls, making detection more challenging as the traffic appears legitimate until the malicious PORT or EPRT command is executed. The potential for data exfiltration via these internal channels poses a severe risk to confidentiality and availability, particularly if sensitive databases or administrative interfaces are accessible on those internal ports.
To mitigate this vulnerability, organizations must prioritize applying the latest security patches provided by IBM as soon as possible. These updates contain code changes that enforce stricter validation rules on FTP command parameters, ensuring that only authorized IP ranges can be used for active data connections. In addition to patching, administrators should implement network-level controls such as firewall rules that restrict outbound connection attempts from the FTP service host to non-essential internal subnets. Monitoring logs for unusual patterns in PORT and EPRT commands can also aid in early detection of exploitation attempts. It is crucial to maintain strict access control policies for FTP services, ensuring that only necessary users have authentication credentials and that these credentials are rotated regularly to minimize the window of opportunity for an attacker who may have compromised valid accounts through other means.