CVE-2017-6594 in Heimdal
Summary
by MITRE
The transit path validation code in Heimdal before 7.3 might allow attackers to bypass the capath policy protection mechanism by leveraging failure to add the previous hop realm to the transit path of issued tickets.
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Analysis
by VulDB Data Team • 12/16/2022
The vulnerability identified as CVE-2017-6594 resides within the Heimdal implementation of the Kerberos authentication system, specifically affecting versions prior to 7.3. This flaw represents a significant weakness in the transit path validation mechanism that governs how authentication tickets traverse multiple realms within a Kerberos environment. The issue stems from the failure of the system to properly validate the complete transit path when tickets are issued across realm boundaries, creating a potential attack vector that could undermine the security posture of organizations relying on cross-realm authentication.
The technical flaw manifests in the capath policy protection mechanism, which is designed to enforce strict validation of authentication paths between realms to prevent unauthorized access through compromised intermediate realms. When the transit path validation code fails to properly incorporate the previous hop realm into the ticket's transit path, it creates an opportunity for attackers to exploit this gap in validation. This vulnerability specifically affects the way Heimdal handles ticket issuance and validation across multiple realms, allowing malicious actors to potentially bypass security controls that should prevent ticket forwarding through unauthorized paths.
The operational impact of this vulnerability extends beyond simple authentication bypass, as it fundamentally undermines the trust model that Kerberos relies upon for cross-realm communications. Attackers could potentially leverage this flaw to escalate privileges by crafting tickets that appear to originate from trusted realms while actually traversing through compromised or unauthorized intermediate realms. This capability directly violates the principle of least privilege and could enable attackers to gain access to resources that should be protected by realm-based access controls, potentially leading to widespread compromise within organizations that depend on Heimdal for authentication services.
Organizations utilizing Heimdal versions prior to 7.3 face significant risk from this vulnerability, particularly those with complex multi-realm authentication environments where cross-realm trust relationships are critical to their security architecture. The vulnerability aligns with CWE-284, which addresses inadequate access control mechanisms, and represents a specific implementation weakness in the Kerberos protocol's security model. From an attacker's perspective, this vulnerability maps to techniques described in the MITRE ATT&CK framework under privilege escalation and lateral movement tactics, where compromised credentials can be used to traverse trust boundaries within a domain environment. The remediation strategy focuses on upgrading to Heimdal version 7.3 or later, which includes corrected transit path validation logic that properly incorporates all intermediate realms into the validation process, thereby restoring the intended security controls and preventing unauthorized path traversal through the authentication system.