CVE-2007-3149 in sudo
Summary
by MITRE
sudo, when linked with MIT Kerberos 5 (krb5), does not properly check whether a user can currently authenticate to Kerberos, which allows local users to gain privileges, in a manner unintended by the sudo security model, via certain KRB5_ environment variable settings. NOTE: another researcher disputes this vulnerability, stating that the attacker must be "a user, who can already log into your system, and can already use sudo."
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Analysis
by VulDB Data Team • 07/20/2021
The vulnerability described in CVE-2007-3149 represents a significant security flaw in the sudo command when integrated with MIT Kerberos 5 authentication system. This issue arises from improper validation of Kerberos authentication status during the privilege escalation process, creating an unexpected pathway for local users to bypass intended security controls. The flaw specifically manifests when certain KRB5_ environment variables are manipulated, allowing attackers to exploit the sudo security model in ways that were not anticipated by the developers. The vulnerability demonstrates a critical gap in the authentication verification process where sudo fails to properly validate that a user has legitimate Kerberos credentials before granting elevated privileges.
The technical implementation of this vulnerability stems from sudo's insufficient verification of Kerberos authentication state when processing environment variables. When sudo is compiled with MIT Kerberos 5 support, it should validate that users possess valid Kerberos tickets before allowing privilege escalation. However, the flaw enables attackers to manipulate KRB5_ environment variables to bypass these checks, effectively allowing unauthorized privilege elevation. This occurs because the sudo command does not adequately enforce Kerberos authentication requirements during the privilege escalation workflow, creating a mismatch between the expected security model and the actual implementation. The vulnerability operates at the intersection of authentication and authorization mechanisms, where environment variable manipulation can override expected security controls.
The operational impact of this vulnerability extends beyond simple privilege escalation to potentially compromise entire system security models. Local users who can manipulate KRB5_ environment variables can gain elevated privileges without proper authentication, effectively undermining the principle of least privilege that sudo is designed to enforce. This creates a dangerous scenario where users who normally have limited access can escalate their privileges to root or other elevated accounts. The vulnerability essentially allows for unauthorized privilege elevation that bypasses the intended security boundaries of the sudo command, potentially leading to complete system compromise. The impact is particularly severe in environments where sudo is used extensively for administrative access control.
Security researchers have noted that this vulnerability requires the attacker to already have local system access and existing sudo privileges, which somewhat limits the attack surface but does not eliminate the risk entirely. The vulnerability aligns with CWE-284, which addresses improper access control, and could be categorized under ATT&CK technique T1548.1 for privilege escalation through sudo manipulation. Mitigation strategies should focus on proper environment variable handling and enhanced Kerberos authentication verification within sudo. System administrators should ensure that sudo is properly configured with restricted environment variables and that Kerberos authentication is properly enforced. Additionally, regular updates to sudo and Kerberos implementations, along with proper access controls and monitoring, can help prevent exploitation of this vulnerability.
The disputed nature of this vulnerability by another researcher highlights the complexity of privilege escalation issues and the importance of understanding the specific attack prerequisites. While the original description suggests a more general vulnerability, the counter-argument emphasizes that the attacker must already have system access and sudo privileges, which narrows the potential attack vectors. This distinction is crucial for security professionals to understand the actual risk level and appropriate mitigation strategies. The vulnerability demonstrates the need for comprehensive security testing that considers both the technical implementation and the operational context in which security controls are applied. Proper system hardening and access control policies remain essential defensive measures against this type of privilege escalation attack.