Cisco Web Security Appliance FTP Authentication Bypass Vulnerability [CVE-2018-0087]
CVE Number – CVE-2018-0087
A vulnerability in the FTP server of the Cisco Web Security Appliance (WSA) could allow an unauthenticated, remote attacker to log in to the FTP server of the device without a valid password. The attacker does need to have a valid username.
The vulnerability is due to incorrect FTP user credential validation. An attacker could exploit this vulnerability by using FTP to connect to the management IP address of the targeted device. A successful exploit could allow the attacker to log in to the FTP server of the Cisco WSA without having a valid password.Cisco has released software updates that address this vulnerability. There are no workarounds that address this vulnerability.
This advisory is available at the following link:
https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20180307-wsa
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Vulnerable Products
This vulnerability affects Cisco AsyncOS for WSA Software on both virtual and hardware appliances that are running any release of Cisco AsyncOS 10.5.1 for WSA Software. See the Fixed Software section of this security advisory for additional information about the affected software releases.
The device is vulnerable only if FTP is enabled on the management interface. FTP is disabled by default.
Determining Whether FTP Is Configured
An administrator can determine whether FTP is configured on the management interface by using one of the following three methods.
First Method to Determine Whether FTP Is Configured
The administrator can issue the showconfig command and check whether the ftpd port is configured on the management interface.
ciscowsa> showconfig Choose the password option: 1. Mask passwords (Files with masked passwords cannot be loaded using loadconfig command) 2. Plain passphrases [1]> 1 . . . <interfaces> <interface> <interface_name>Management</interface_name> <ip>x.x.x.x</ip> <phys_interface>Management</phys_interface> <netmask>24</netmask> <interface_hostname>xxx.xxx.xxx</interface_hostname> <ftpd_port>21</ftpd_port> . . .Second Method to Determine Whether FTP Is Configured
The administrator can check the FTP configuration by issuing the ifconfig command. In this example, the management interface is configured for FTP. The Y value in square brackets represents the current configuration.
ciscowsa> ifconfig . . . Choose the operation you want to perform: - NEW - Create a new interface. - EDIT - Modify an interface. - DELETE - Remove an interface. - DETAILS - Show details of an interface. > EDIT Enter the number of the interface you wish to edit. []> 1 . . Do you want to enable FTP on this interface? [Y]> . . .
Third Method to Determine Whether FTP Is Configured
The administrator can also use the GUI to check the FTP configuration by navigating to Network > Interfaces > Appliance Management Services and determining whether the FTP check box is checked.
Determining the WSA Software Release
To determine whether a vulnerable release of Cisco AsyncOS Software is running on a Cisco WSA, administrators can use the version command in the WSA CLI. The following example shows the results for an appliance that is running Cisco AsyncOS Software Release 10.5.1-296:
ciscowsa> version Current Version =============== Product: Cisco IronPort S670 Web Security Appliance Model: S670 Version: 10.5.1-296 . . .
Products Confirmed Not Vulnerable
No other Cisco products are currently known to be affected by this vulnerability.
The following products are not affected by this vulnerability:
- Email Security Appliance (ESA), both virtual and hardware versions
- Security Mail Appliance (SMA), both virtual and hardware versions
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There are no workarounds that address this vulnerability. However, this vulnerability exists only when FTP is enabled on the management interface. If FTP is disabled, this vulnerability does not exist; therefore, disabling FTP is considered a mitigation for the vulnerability.
Disabling FTP on the Management Interface
An administrator can disable FTP on the management interface by using one of the following two methods.
First Method to Disable FTP on the Management Interface
The administrator can disable FTP by issuing the ifconfig command to edit the management interface configuration and then issuing the commit command to commit the change.
ciscowsa> ifconfig . . . Choose the operation you want to perform: - NEW - Create a new interface. - EDIT - Modify an interface. - DELETE - Remove an interface. - DETAILS - Show details of an interface. > EDIT Enter the number of the interface you wish to edit. []> 1 . . Do you want to enable FTP on this interface? [Y]> N . . . Choose the operation you want to perform: - NEW - Create a new interface. - EDIT - Modify an interface. - DELETE - Remove an interface. - DETAILS - Show details of an interface. []> ciscowsa> commit Warning: In order to process these changes, the proxy process will restart after Commit. This will cause a brief interruption in service. Additionally, the authentication cache will be cleared, which might require some users to authenticate again. Warning: Processing of network configuration changes might cause a brief interruption in network availability. Please enter some comments describing your changes: []> disable FTP Changes committed . . .
Second Method to Disable FTP on the Management InterfaceThe administrator can disable FTP from the GUI by navigating to Network > Interfaces > Appliance Management Services and unchecking the FTP check box, then clicking Submit to commit the change.
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Cisco has released free software updates that address the vulnerability described in this advisory. Customers may only install and expect support for software versions and feature sets for which they have purchased a license. By installing, downloading, accessing, or otherwise using such software upgrades, customers agree to follow the terms of the Cisco software license: http://www.cisco.com/en/US/docs/general/warranty/English/EU1KEN_.html
Additionally, customers may only download software for which they have a valid license, procured from Cisco directly, or through a Cisco authorized reseller or partner. In most cases this will be a maintenance upgrade to software that was previously purchased. Free security software updates do not entitle customers to a new software license, additional software feature sets, or major revision upgrades.
When considering software upgrades, customers are advised to regularly consult the advisories for Cisco products, which are available from the Cisco Security Advisories and Alerts page, to determine exposure and a complete upgrade solution.
In all cases, customers should ensure that the devices to be upgraded contain sufficient memory and confirm that current hardware and software configurations will continue to be supported properly by the new release. If the information is not clear, customers are advised to contact the Cisco Technical Assistance Center (TAC) or their contracted maintenance providers.
Customers Without Service Contracts
Customers who purchase directly from Cisco but do not hold a Cisco service contract and customers who make purchases through third-party vendors but are unsuccessful in obtaining fixed software through their point of sale should obtain upgrades by contacting the Cisco TAC: http://www.cisco.com/en/US/support/tsd_cisco_worldwide_contacts.html
Customers should have the product serial number available and be prepared to provide the URL of this advisory as evidence of entitlement to a free upgrade.
Fixed Releases
In the following table, the left column lists major releases of Cisco AsyncOS for WSA Software. The right column indicates whether a major release is affected by the vulnerability described in this advisory and the first minor release that includes the fix for this vulnerability.
Customers should upgrade to an appropriate release as indicated in the following table:
Cisco AsyncOS for WSA Software Major Release First Fixed Release for This Advisory Prior to 10.5.1 Not vulnerable 10.5.1 10.5.2-042 or later 11.0 and later Not vulnerable In most cases, a WSA can be updated over the network by using the System Upgrade options in the System Administration GUI. Administrators can use the following steps to upgrade a device by using the System Administration GUI:
- Choose System Administration > System Upgrade.
- Click Upgrade Options.
- Choose Download and Install.
- Choose the release to upgrade to.
- In the Upgrade Preparation area, choose the appropriate options.
- Click Proceed to begin the upgrade. A progress bar displays the status of the upgrade.
After the upgrade is complete, the device reboots.
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The Cisco Product Security Incident Response Team (PSIRT) is not aware of any public announcements or malicious use of the vulnerability that is described in this advisory.
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This vulnerability was found during resolution of a Cisco TAC support case.
Duncan is a technology professional with over 20 years experience of working in various IT roles. He has a interest in cyber security, and has a wide range of other skills in radio, electronics and telecommunications.