CVE-2001-1380 in OpenSSH
Summary
by MITRE
OpenSSH before 2.9.9, while using keypairs and multiple keys of different types in the ~/.ssh/authorized_keys2 file, may not properly handle the "from" option associated with a key, which could allow remote attackers to login from unauthorized IP addresses.
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Analysis
by VulDB Data Team • 12/26/2024
The vulnerability described in CVE-2001-1380 represents a critical authorization flaw in OpenSSH versions prior to 2.9.9 that affects the handling of key-based authentication mechanisms. This issue specifically impacts the configuration file ~/.ssh/authorized_keys2 where multiple SSH keys of different types can be stored and managed. The vulnerability stems from improper processing of the "from" option that is associated with individual keys within this file, creating a potential security bypass that allows unauthorized remote access attempts from IP addresses that should be restricted.
The technical flaw manifests when OpenSSH processes multiple keys in the authorized_keys2 file and fails to properly validate the "from" restriction clause for each key entry. This misconfiguration enables attackers to exploit the key management system by crafting authentication requests that bypass the intended IP address restrictions. The "from" option in SSH key configuration is designed to limit which IP addresses can successfully authenticate using a particular key, but due to this flaw, the system does not properly enforce these restrictions, effectively nullifying the security controls that administrators implement to limit access based on source IP addresses.
From an operational impact perspective, this vulnerability creates a significant risk for systems relying on SSH key-based authentication with IP-based restrictions. Attackers can leverage this flaw to authenticate from unauthorized IP addresses, potentially gaining access to systems that were configured to restrict access to specific networks or IP ranges. The vulnerability affects the fundamental security principle of least privilege and can lead to unauthorized system access, data exfiltration, and potential lateral movement within network environments where SSH access is used for administrative purposes. This issue particularly impacts environments where network segmentation and IP-based access controls are implemented as part of security policies.
The mitigation strategy for this vulnerability requires immediate upgrading to OpenSSH version 2.9.9 or later, which contains the necessary fixes to properly handle the "from" option in key configurations. Administrators should also review existing authorized_keys2 files to ensure that IP-based restrictions are properly implemented and tested. Additional security measures include implementing additional authentication layers such as two-factor authentication, regularly auditing SSH access logs, and monitoring for unauthorized access attempts. This vulnerability aligns with CWE-284 which addresses improper access control, and relates to ATT&CK technique T1078.004 which covers valid accounts with restricted access. Organizations should also consider implementing network-based controls such as firewall rules and intrusion detection systems to provide additional layers of defense against exploitation attempts. The remediation process should include thorough testing of key configurations to ensure that the fix properly enforces IP-based restrictions and that legitimate access is not disrupted.