CVE-2015-3206 in python-kerberos
Summary
by MITRE
The checkPassword function in python-kerberos does not authenticate the KDC it attempts to communicate with, which allows remote attackers to cause a denial of service (bad response), or have other unspecified impact by performing a man-in-the-middle attack.
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Analysis
by VulDB Data Team • 12/16/2022
The vulnerability identified as CVE-2015-3206 resides within the python-kerberos library's checkPassword function, which operates under the Kerberos authentication protocol framework. This flaw represents a critical security weakness in the authentication process where the system fails to verify the identity of the Key Distribution Center (KDC) during communication. The absence of KDC authentication creates a significant attack surface that adversaries can exploit to manipulate the authentication flow. Kerberos authentication relies on mutual authentication between the client and server to ensure that both parties are legitimate participants in the authentication process. When this mutual verification is absent, the client becomes vulnerable to various forms of malicious interference.
The technical implementation of this vulnerability stems from the lack of certificate validation or hostname verification within the checkPassword function. In standard Kerberos implementations, the client should validate that the KDC it communicates with is the legitimate server and not an imposter. This validation typically involves checking digital certificates against trusted certificate authorities or verifying hostnames against expected values. Without these security checks, an attacker positioned between the client and the legitimate KDC can intercept and manipulate authentication messages. The attacker can respond to authentication requests with forged responses, potentially causing the client to accept invalid credentials or simply fail to establish authentication altogether.
The operational impact of this vulnerability extends beyond simple denial of service conditions to encompass more severe security implications. An attacker can exploit this weakness to perform man-in-the-middle attacks that may result in unauthorized access to systems protected by Kerberos authentication. The unspecified impact mentioned in the CVE description suggests that beyond the immediate denial of service, attackers might be able to manipulate authentication decisions, potentially leading to privilege escalation or complete system compromise. This vulnerability affects any application or system that relies on python-kerberos for authentication and communicates with Kerberos-enabled services. The attack vector requires network access to intercept communications between the client and KDC, making it particularly dangerous in environments where network traffic is not properly secured or monitored.
Organizations utilizing python-kerberos for authentication should implement immediate mitigations to address this vulnerability. The most effective approach involves updating to a patched version of the python-kerberos library that implements proper KDC authentication mechanisms. Security practitioners should also consider implementing network-level protections such as encrypted communication channels, network segmentation, and monitoring for unusual authentication patterns. Additionally, organizations should review their Kerberos configuration to ensure that proper certificate validation and hostname verification are enabled. This vulnerability aligns with CWE-295, which addresses improper certificate validation, and maps to ATT&CK technique T1550.003 for use of Kerberoasting, as it undermines the fundamental security assumptions of the Kerberos protocol. The vulnerability demonstrates the critical importance of maintaining proper authentication protocols and the potential consequences when cryptographic verification mechanisms are bypassed or omitted from security implementations.