CVE-2017-11103 in macOS
Summary
by MITRE
Heimdal before 7.4 allows remote attackers to impersonate services with Orpheus' Lyre attacks because it obtains service-principal names in a way that violates the Kerberos 5 protocol specification. In _krb5_extract_ticket() the KDC-REP service name must be obtained from the encrypted version stored in 'enc_part' instead of the unencrypted version stored in 'ticket'. Use of the unencrypted version provides an opportunity for successful server impersonation and other attacks. NOTE: this CVE is only for Heimdal and other products that embed Heimdal code; it does not apply to other instances in which this part of the Kerberos 5 protocol specification is violated.
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Analysis
by VulDB Data Team • 01/05/2023
The vulnerability described in CVE-2017-11103 represents a critical flaw in the Heimdal Kerberos implementation that fundamentally undermines the security assurances provided by the Kerberos 5 protocol. This issue affects Heimdal versions prior to 7.4 and stems from improper handling of service principal names during ticket processing, creating a pathway for sophisticated impersonation attacks that align with the Orpheus' Lyre attack methodology. The flaw specifically manifests in the _krb5_extract_ticket() function where the implementation violates established Kerberos protocol specifications by extracting service names from the wrong location within the ticket structure.
The technical root cause of this vulnerability lies in the improper extraction of service principal names from Kerberos ticket structures. According to the Kerberos 5 protocol specification, the service name contained in the KDC-REP (Kerberos Distribution Center Reply) must be obtained from the encrypted portion stored within the 'enc_part' field rather than from the unencrypted 'ticket' field. This deviation from the standard creates a significant security gap because the unencrypted version can be manipulated by attackers without requiring cryptographic keys. The violation directly contravenes the Kerberos protocol's design principles for maintaining authentication integrity and service identity verification, as outlined in the Kerberos Network Authentication Service Protocol specification.
The operational impact of this vulnerability extends far beyond simple authentication bypasses, as it enables sophisticated service impersonation attacks that can compromise entire authentication domains. Attackers can exploit this weakness to impersonate legitimate services within the Kerberos realm, potentially gaining unauthorized access to protected resources and systems. The Orpheus' Lyre attack pattern specifically leverages such vulnerabilities by manipulating the service principal name extraction process to redirect authentication requests to malicious endpoints. This capability allows adversaries to perform man-in-the-middle attacks, service substitution, and credential harvesting that can persist across multiple authentication sessions. The vulnerability affects the fundamental trust model of Kerberos implementations, undermining the protocol's core security guarantees and potentially enabling lateral movement within networks that rely on Heimdal for authentication services.
Organizations utilizing Heimdal prior to version 7.4 face significant risk exposure from this vulnerability, particularly in environments where Kerberos authentication is critical for system security. The attack vector is remote and requires no privileged access, making it particularly dangerous as it can be exploited from any network location where the vulnerable service is accessible. Security practitioners should consider this vulnerability in the context of the MITRE ATT&CK framework, specifically noting its relationship to privilege escalation and defense evasion techniques that rely on authentication manipulation. The vulnerability aligns with ATT&CK technique T1550.003 (Use Alternate Authentication Material) and T1550.002 (Pass the Hash), as it enables attackers to effectively bypass authentication mechanisms through service name manipulation. The remediation strategy focuses on upgrading to Heimdal version 7.4 or later, which properly implements the Kerberos 5 specification by extracting service principal names from the encrypted enc_part field. Additionally, organizations should conduct thorough security assessments of their Kerberos implementations to identify any other potential code paths that may exhibit similar violations of the Kerberos protocol specification. The vulnerability serves as a reminder of the critical importance of strict adherence to established protocol specifications in security implementations, as deviations even in seemingly minor components can create substantial attack surfaces that compromise entire authentication infrastructures.