CVE-2021-38993 in AIX
Summary
by MITRE • 02/25/2022
IBM AIX 7.1, 7.2, 7.3, and VIOS 3.1 could allow a non-privileged local user to exploit a vulnerability in the smbcd daemon to cause a denial of service. IBM X-Force ID: 212962.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 02/28/2022
The vulnerability identified as CVE-2021-38993 affects IBM AIX operating systems version 7.1, 7.2, 7.3, and VIOS 3.1 platforms, specifically targeting the smbcd daemon component. This daemon is responsible for handling Server Message Block file sharing services within the AIX environment, making it a critical component for network file access and sharing operations. The flaw represents a local denial of service vulnerability that can be exploited by unprivileged users who have access to the system, potentially compromising the availability of file sharing services and disrupting normal business operations. The vulnerability stems from improper input validation within the smbcd daemon implementation, creating a condition where malformed or specially crafted input can cause the daemon to crash or become unresponsive.
From a technical perspective, this vulnerability manifests through inadequate error handling mechanisms within the smbcd daemon's processing of network requests. The daemon fails to properly validate incoming data structures or parameter values, allowing malicious input to trigger unexpected behavior in the service's execution flow. This type of vulnerability typically falls under CWE-129, which addresses insufficient input validation, and may also relate to CWE-20, representing input validation issues that can lead to various security consequences. The exploitation requires local access to the system and does not involve network-based attacks, but the impact on service availability makes it particularly concerning for enterprise environments where file sharing services are heavily utilized. The vulnerability affects systems where the smbcd daemon is actively running and handling file sharing requests, creating a potential disruption point for critical business operations.
The operational impact of this vulnerability extends beyond simple service disruption, as it can affect the reliability and availability of file sharing services that many applications and users depend upon. When the smbcd daemon crashes or becomes unresponsive, it can interrupt file access for multiple users and applications simultaneously, potentially causing cascading effects throughout the enterprise infrastructure. Organizations running AIX systems with active file sharing services face significant risk, particularly in environments where continuous availability is critical for business operations. The vulnerability can be exploited by any local user with basic system access, making it particularly dangerous in multi-user environments where access controls may not be strictly enforced. This type of local denial of service attack aligns with ATT&CK technique T1499.004, which covers network denial of service attacks, though in this case the attack vector is local rather than network-based.
Organizations should implement immediate mitigations to address this vulnerability, including applying the relevant IBM security patches and updates as provided in their security bulletins. System administrators should also consider implementing additional monitoring of the smbcd daemon's behavior to detect potential exploitation attempts, as well as reviewing and strengthening local access controls to limit potential attack vectors. The vulnerability's nature suggests that disabling or restricting access to the smbcd daemon service may be a viable temporary mitigation strategy while permanent patches are deployed. Regular security assessments should include verification that the smbcd daemon is properly patched and that appropriate access controls are in place to prevent unauthorized local access to systems where this service operates. Additionally, organizations should ensure that their incident response procedures include specific guidance for handling local denial of service attacks targeting system services like the smbcd daemon, as these incidents can significantly impact operational continuity and require immediate attention to restore service availability.