CVE-2019-12098 in Heimdal
Summary
by MITRE
In the client side of Heimdal before 7.6.0, failure to verify anonymous PKINIT PA-PKINIT-KX key exchange permits a man-in-the-middle attack. This issue is in krb5_init_creds_step in lib/krb5/init_creds_pw.c.
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Analysis
by VulDB Data Team • 04/16/2026
The vulnerability described in CVE-2019-12098 represents a critical security flaw in the Heimdal Kerberos implementation that affects versions prior to 7.6.0. This issue specifically impacts the client-side authentication process within the Kerberos protocol, where the anonymous PKINIT PA-PKINIT-KX key exchange mechanism fails to properly verify the authenticity of the key exchange. The flaw exists in the krb5_init_creds_step function located in the lib/krb5/init_creds_pw.c source file, which is responsible for handling the initialization of Kerberos credentials during the password-based authentication process. The vulnerability creates a significant attack surface that allows malicious actors to intercept and manipulate the authentication flow without proper verification of the key exchange parameters.
The technical nature of this vulnerability stems from the absence of proper validation during the anonymous PKINIT key exchange phase, which is designed to establish secure communication channels between clients and Kerberos servers. When the client performs the PA-PKINIT-KX key exchange without verifying the server's credentials or the integrity of the key exchange process, it opens the door for man-in-the-middle attacks. This weakness allows attackers to position themselves between the legitimate client and server, potentially intercepting or modifying authentication tokens and credentials. The vulnerability is particularly dangerous because it operates at the protocol level where trust is established, making it difficult to detect without deep protocol analysis.
The operational impact of CVE-2019-12098 extends beyond simple credential theft, as it fundamentally undermines the security guarantees that Kerberos authentication is designed to provide. Attackers exploiting this vulnerability can potentially impersonate legitimate users, gain unauthorized access to protected resources, and compromise the entire Kerberos domain. The man-in-the-middle attack capability means that even if users believe they are authenticating to a legitimate server, they may actually be communicating with an attacker's system. This vulnerability affects organizations that rely heavily on Kerberos-based authentication systems, particularly those using Heimdal implementations in enterprise environments where secure authentication is critical for maintaining access control and data integrity. The attack vector is particularly concerning because it can be executed without requiring prior knowledge of user credentials or complex attack infrastructure.
Organizations should immediately upgrade to Heimdal version 7.6.0 or later to address this vulnerability, as the fix implements proper verification of the anonymous PKINIT key exchange mechanism. Security teams should also conduct thorough network monitoring to detect potential exploitation attempts and implement additional layers of authentication verification. The vulnerability aligns with CWE-310, which addresses cryptographic weaknesses in key exchange mechanisms, and represents a clear violation of the principle of least privilege and authentication integrity. From an ATT&CK perspective, this vulnerability maps to techniques involving credential access and defense evasion, as attackers can leverage it to establish persistent access while remaining undetected. Organizations should also review their Kerberos configurations and implement additional security controls such as certificate-based authentication and network segmentation to mitigate the risk of exploitation.