CVE-2011-1526 in Kerberos
Summary
by MITRE
ftpd.c in the GSS-API FTP daemon in MIT Kerberos Version 5 Applications (aka krb5-appl) 1.0.1 and earlier does not check the krb5_setegid return value, which allows remote authenticated users to bypass intended group access restrictions, and create, overwrite, delete, or read files, via standard FTP commands, related to missing autoconf tests in a configure script.
Be aware that VulDB is the high quality source for vulnerability data.
Analysis
by VulDB Data Team • 11/14/2021
The vulnerability described in CVE-2011-1526 resides within the GSS-API FTP daemon implementation of MIT Kerberos Version 5 Applications, specifically in the ftpd.c source file. This flaw affects versions 1.0.1 and earlier, representing a critical security oversight in the authentication and authorization mechanisms of the FTP service. The vulnerability stems from insufficient error handling within the daemon's privilege management code, creating a pathway for authenticated attackers to escalate their privileges beyond intended restrictions.
The technical root cause of this vulnerability is the failure to properly validate the return value of the krb5_setegid function call within the FTP daemon's execution flow. This function is responsible for setting the effective group ID of the process, which directly controls file access permissions and directory traversal capabilities. When the return value is not checked, the daemon continues execution regardless of whether the group ID change was successful or failed, leading to an inconsistent security state where the process maintains elevated privileges despite failed authorization attempts. This represents a classic example of improper error handling as classified under CWE-754, where a security-relevant function call does not properly validate its return status.
The operational impact of this vulnerability is severe and multifaceted, as it allows remote authenticated users to bypass intended group access restrictions entirely. Attackers can leverage this flaw to perform unauthorized file operations including creating, overwriting, deleting, or reading files within the FTP service's directory structure. This effectively undermines the principle of least privilege and can lead to complete compromise of the file system access controlled by the FTP daemon. The vulnerability is particularly dangerous because it requires only authentication to the FTP service, making it exploitable by anyone with valid credentials, and the attack does not require special privileges beyond standard user access. This aligns with ATT&CK technique T1078.002, which covers legitimate credentials and valid accounts as a means of gaining access.
The vulnerability is further exacerbated by missing autoconf tests in the configure script, indicating that the build process did not properly validate the system's capabilities or that the necessary security checks were omitted during compilation. This suggests that the vulnerability may have been introduced during the build configuration phase rather than being a runtime error, making it more difficult to detect and remediate. The lack of proper build-time validation creates a scenario where the daemon may be compiled with incomplete security features or without necessary privilege checks. Organizations should implement comprehensive build validation processes to ensure that all security-relevant tests are properly executed during the software compilation phase, as recommended by the NIST SP 800-160 standard for secure software development practices.
Mitigation strategies should include immediate patching of affected systems to version 1.0.2 or later of MIT Kerberos Applications, which contains the necessary fixes for the krb5_setegid return value checking. System administrators should also implement monitoring for unauthorized file access patterns and privilege escalation attempts. The vulnerability highlights the importance of proper error handling in security-critical code paths and emphasizes the need for thorough testing of privilege management functions. Additionally, organizations should conduct comprehensive audits of their FTP services and Kerberos implementations to identify similar vulnerabilities in other components of their authentication infrastructure. The fix for this vulnerability demonstrates the critical nature of ensuring that all system calls which affect security posture are properly validated and that error conditions are appropriately handled to maintain system integrity.