CVE-2026-117548 in Directory Server
Summary
by MITRE • 10/29/2026
A NULL pointer dereference flaw was found in 389-ds-base. This flaw occurs when a ModifyDN (rename) operation uses an attribute's schema alias name (such as "commonName") instead of its canonical name (such as "cn") as the new relative distinguished name. An authenticated attacker with the ModifyDN (rename) permission on the affected entry can use this flaw to crash the directory server, causing a denial of service.
Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.
Analysis
by VulDB Data Team • 10/29/2026
The vulnerability identified in 389-ds-base represents a critical stability issue within the Directory Server software, specifically manifesting during attribute modification operations that involve renaming entries. This flaw is categorized as a NULL pointer dereference, which corresponds to CWE-476 in the Common Weakness Enumeration taxonomy. The technical root cause lies in how the server processes schema alias names versus canonical names when executing a ModifyDN operation. In LDAP directory services, attributes often have both a human-readable alias name and an internal canonical identifier. For instance, while users typically refer to "commonName," the system internally recognizes it as "cn." When an administrator or application performs a rename operation using the alias form for the new relative distinguished name rather than the standardized canonical form, the underlying code fails to properly resolve the attribute type before attempting to access its associated data structures. This oversight results in the program attempting to dereference a memory address that holds no valid value, triggering a segmentation fault and causing an immediate crash of the directory server process.
From an operational perspective, this vulnerability poses a significant risk to service availability. Because the flaw is triggered by a specific sequence of operations involving schema alias usage during entry renaming, it allows for a targeted denial-of-service attack. An authenticated attacker who possesses the ModifyDN permission on any affected entry can exploit this condition to crash the server instance. In enterprise environments where 389-ds-base serves as the primary identity provider or authentication backend, such an outage disrupts access control mechanisms, prevents user logins, and halts dependent applications that rely on directory queries for authorization decisions. The impact is not limited to a single session but affects all users connected to the server until it is manually restarted by system administrators, leading to prolonged downtime and potential data inconsistency if transactions were in progress during the crash.
The exploitation of this vulnerability aligns with MITRE ATT&CK techniques related to resource exhaustion or service disruption, specifically falling under the category of Denial of Service against critical infrastructure services. While the attacker requires authentication, which limits the attack surface compared to unauthenticated exploits, it remains a serious concern for internal threats or compromised accounts within an organization's directory structure. The requirement for ModifyDN permissions means that any user with rights to rename objects in specific parts of the directory tree can trigger this condition. This highlights the importance of least-privilege principles and rigorous validation of input parameters even from authenticated sources, as administrative functions are often targeted by insiders or compromised credentials seeking to cause maximum disruption.
Mitigation strategies for this vulnerability primarily involve applying vendor-provided patches that address the code path responsible for handling schema alias resolution during ModifyDN operations. Administrators should ensure their 389-ds-base installations are updated to versions where this logic error has been corrected, ensuring that both canonical and alias names are handled consistently without leading to null pointer access. In addition to patching, organizations can implement operational safeguards such as monitoring server logs for segmentation faults or unexpected process restarts to detect potential exploitation attempts early. Furthermore, reviewing user permissions to ensure that only essential personnel have ModifyDN rights on critical directory entries reduces the attack surface. Regular security audits and adherence to secure coding practices within internal applications interacting with the directory service can also prevent accidental triggers of this flaw by ensuring canonical names are used in all LDAP operations where possible.