Cisco IOS Software contains a vulnerability in the FTP server feature that could allow an unauthenticated, remote attacker to bypass authentication and gain complete control over a device. The vulnerable FTP server feature exists in a limited number of IOS trains.
The vulnerability exists due to a lack of proper authorization verification in the Cisco IOS FTP server feature. An unauthenticated, remote attacker could exploit this vulnerability to gain unauthorized access to the Cisco IOS file system. An attacker could leverage this access to create a denial of service (DoS) condition or execute arbitrary code with elevated privileges.
Proof-of-concept code is available.
Cisco confirmed this vulnerability in a security advisory and released updated software.
Indicators of Compromise
Cisco has published a list of affected IOS products in the security advisory.
The vulnerability exists because the Cisco IOS FTP server feature that exists in a limited number of Cisco IOS release trains fails to perform proper authentication checking. An unauthenticated, remote attacker could exploit this vulnerability to access the file system of a device. Successful exploitation could allow the attacker to gain read and write access to the file system that was configured to use the FTP server feature.
The Cisco IOS FTP feature allows administrators to store arbitrary files on a device's flash file system. Administrators often use this feature to stage configurations and software images for devices that are located in a regional area to reduce the amount of traffic that traverses an enterprise's core network. Because this feature also includes access to the affected device's startup script and running firmware, an attacker could replace or modify these files. File modification could allow the attacker to execute arbitrary code or commands on the device when it is restarted.
A remote attacker could trigger a restart of the device by exploiting the FTP server feature DoS vulnerability documented in Alert 13159.
Cisco rates the exploitability of this vulnerability as functional. However, no publicly available functional exploit code is known to exist. The available proof-of-concept code was designed to allow code execution only in certain specialized circumstances.
The Cisco IOS FTP server is considered insecure and is being deprecated. The update from Cisco removes the FTP server feature from affected Cisco IOS Software releases.
Administrators are advised to apply the appropriate update.
Administrators may consider migrating to a version of Cisco IOS Software that does not incorporate the FTP server option.
Administrators are advised to disable the Cisco IOS FTP server by issuing the following command:
no ftp-server enable
Administrators may consider alternate means of transferring files, such as Secure Copy (SCP) or a Trivial File Transfer Protocol (TFTP) server.
Administrators are advised to implement infrastructure and receive access control lists (ACLs).
Administrators are advised to implement the Control Plane Policing (CoPP) feature of Cisco IOS Software on supported devices.
The Cisco Applied Intelligence team has created the following companion document to guide administrators in identifying and mitigating attempts to exploit this vulnerability prior to applying updated software: cisco-air-20070509-iosftp
Cisco customers with active contracts can obtain updates through the Software Center at the following link: Cisco. Cisco customers without contracts can obtain upgrades by contacting the Cisco Technical Assistance Center at 1-800-553-2447 or 1-408-526-7209 or via e-mail at firstname.lastname@example.org.
Proof-of-concept code is available for the FTP server authentication bypass vulnerability in Cisco IOS Software. Cisco has released an additional bug ID.
2008-July-29 18:57 GMT
Cisco IOS Software contains a vulnerability in the FTP server component that could allow an unauthenticated, remote attacker to bypass authentication and gain complete control over the affected device. Updates are available.
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