CVE-2018-14629 in Samba
Summary
by MITRE
A denial of service vulnerability was discovered in Samba's LDAP server before versions 4.7.12, 4.8.7, and 4.9.3. A CNAME loop could lead to infinite recursion in the server. An unprivileged local attacker could create such an entry, leading to denial of service.
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Analysis
by VulDB Data Team • 06/12/2023
The vulnerability identified as CVE-2018-14629 represents a critical denial of service flaw within Samba's Lightweight Directory Access Protocol implementation that affected multiple versions prior to the security releases of 4.7.12, 4.8.7, and 4.9.3. This issue stems from insufficient validation of DNS record processing within the LDAP server component, creating a scenario where maliciously crafted entries could trigger recursive lookup behaviors that consume system resources indefinitely. The flaw specifically manifests when the LDAP server encounters a CNAME (Canonical Name) record that references itself or creates a circular dependency chain, leading to unbounded recursion during DNS resolution operations.
The technical mechanism behind this vulnerability operates through the LDAP server's handling of DNS queries and record resolution processes. When processing directory entries containing CNAME records that form loops or circular references, the server's DNS resolution logic fails to detect and terminate these recursive patterns, causing the system to enter an infinite loop of DNS lookups. This recursive behavior consumes CPU cycles and memory resources without termination, effectively rendering the LDAP service unavailable to legitimate users. The vulnerability is particularly dangerous because it requires no authentication to exploit, making it accessible to any local user with minimal privileges who can modify LDAP directory entries.
From an operational perspective, this vulnerability presents a significant risk to organizations relying on Samba for directory services, as it allows unprivileged attackers to disrupt critical authentication and authorization services. The denial of service impact extends beyond simple service interruption to potentially affecting enterprise-wide authentication systems, user access to resources, and overall network availability. The vulnerability's exploitation does not require elevated privileges, making it particularly concerning for environments where local user access is not properly restricted. Security incidents involving this flaw could result in extended downtime, service degradation, and potential cascading effects on dependent systems that rely on Samba's LDAP functionality.
The vulnerability aligns with CWE-674, which addresses "Uncontrolled Recursion" in software systems, and can be mapped to ATT&CK technique T1499.004, which covers "Endpoint Denial of Service" through resource exhaustion. Organizations should implement immediate mitigations including applying the relevant security patches to versions 4.7.12, 4.8.7, and 4.9.3, along with implementing additional monitoring for unusual DNS lookup patterns and recursive behavior in LDAP services. Network segmentation and access controls should be strengthened to limit local user privileges and prevent unauthorized modification of directory entries. System administrators should also configure logging and alerting mechanisms to detect potential exploitation attempts and monitor for signs of resource exhaustion or abnormal recursive DNS resolution patterns.