CVE-2026-58216

An out-of-bounds read flaw was found in Samba's Kerberos Key Distribution Center's (KDC) password change (kpasswd) service. When processing malformed ASN.1-encoded Kerberos password change request, Samba server miscalculates the structure size and attempts to read up to six bytes beyond the end of the allocated buffer. While this out-of-bounds read typically results in a harmless decryption failure, if the read hits unmapped memory, it causes the KDC process to crash. An authenticated attacker can send a specially crafted kpasswd request containing malformed ASN.1 data to trigger the out-of-bounds read, which may cause the KDC process to terminate, resulting in a denial of service.

Red Hat Product Security has rated this vulnerability as having a Moderate security impact.

Successful exploitation requires an authenticated attacker to craft a malformed ASN.1-encoded Kerberos password change request that precisely triggers the underlying parsing flaw, increasing the attack complexity. The Samba project also notes that the attack is unreliable in practice and an attacker may need to perform numerous kpasswd attempts before successfully causing the service to terminate.

Standard RHEL Server Deployments (Not Affected): Default Red Hat Enterprise Linux (RHEL) deployments are not affected. RHEL does not support the Samba Active Directory Domain Controller (AD DC) role or its integrated Kerberos Key Distribution Center (KDC), including the kpasswd service, where this vulnerability resides.

Samba AD DC Deployments (Affected): Deployments explicitly configured to operate as a Samba Active Directory Domain Controller (server role = active directory domain controller) are affected.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.