CVE-2000-0575 in SSH
Summary
by MITRE
SSH 1.2.27 with Kerberos authentication support stores Kerberos tickets in a file which is created in the current directory of the user who is logging in, which could allow remote attackers to sniff the ticket cache if the home directory is installed on NFS.
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Analysis
by VulDB Data Team • 05/05/2019
The vulnerability described in CVE-2000-0575 represents a critical security flaw in SSH version 1.2.27 that specifically affects systems utilizing Kerberos authentication. This issue stems from improper handling of Kerberos ticket storage mechanisms within the SSH implementation, creating a significant attack vector for remote adversaries. The flaw manifests when SSH processes create Kerberos ticket cache files in the user's current working directory rather than in secure, isolated locations, fundamentally undermining the security model designed to protect authentication credentials.
The technical implementation of this vulnerability involves the SSH daemon's failure to properly secure Kerberos ticket files during authentication processes. When users authenticate via Kerberos through SSH, the system generates ticket cache files that contain sensitive authentication tokens necessary for accessing network services. These files are created with predictable naming conventions and are placed in the user's current directory, which may be a network-mounted filesystem such as NFS. The insecure placement of these files creates a race condition and exposure scenario where unauthorized parties can access or intercept the ticket cache data.
The operational impact of this vulnerability extends beyond simple credential theft to encompass broader network compromise scenarios. When home directories are mounted via NFS, the ticket cache files become accessible to any user with read permissions on the shared filesystem, potentially allowing attackers to obtain valid Kerberos tickets for other users. This creates a pathway for lateral movement within networks, privilege escalation, and persistent access to protected services. The vulnerability specifically targets environments where NFS is used for home directory storage, making it particularly dangerous in enterprise settings where such configurations are common.
The security implications align with CWE-310, which addresses cryptographic issues related to improper handling of sensitive data, and reflects patterns commonly found in the ATT&CK framework under credential access and privilege escalation techniques. Attackers can leverage this vulnerability through passive network monitoring or active filesystem reconnaissance to capture ticket cache files, then use these credentials to authenticate as legitimate users without requiring knowledge of user passwords. This makes the vulnerability particularly dangerous because it operates at the authentication layer rather than requiring initial access through other attack vectors.
Mitigation strategies should focus on implementing secure file handling practices for Kerberos ticket storage, including enforcing proper file permissions and ensuring ticket cache files are created in secure, isolated locations rather than user directories. Organizations should consider disabling Kerberos authentication in SSH when NFS is used for home directories or implement additional network segmentation to isolate authentication services. The most effective remediation involves updating to SSH versions that properly handle Kerberos ticket cache files in secure locations and implementing monitoring for unauthorized access to authentication cache files. Additionally, network administrators should review NFS mount configurations and ensure proper access controls are in place to prevent unauthorized file system access to user directories containing sensitive authentication data.