Privilege Escalation Flaw Discovered in the Cisco Adaptive Security Appliance

Tenable has discovered a privilege escalation flaw in the Cisco Adaptive Security Appliance that allows low-level users to run higher-level commands when certain configuration settings are set.

• What you need to know: An authenticated remote unprivileged user can change or download the running configuration or replace the appliance firmware where they shouldn’t.
• What’s the attack vector? HTTP Requests
• What’s the business impact? Attackers could read or write files on the system, overwrite firmware and create new users.
• What’s the solution? Update to the latest version of Cisco IOS.

Background

Tenable has discovered privilege escalation flaws in the Cisco Adaptive Security Appliance (ASAv) 9.9.2. Cisco has assigned this issue CVE-2018-15465. This flaw would allow users with the lowest privilege level of 1 to potentially overwrite the system's firmware, request the full configuration file, and create new users with privilege level 15. It requires the HTTP interface for IOS to be enabled, and the “aaa” authentication scheme needs to be set, which is not part of the ASAv default configuration.

Cisco’s ASAv is a virtual machine (VM) with nearly identical features to the company’s physical ASA, which are network security devices that provide firewall, intrusion prevention and private network (VPN) capabilities. The ASAv has additional features for clustering and multiple contexts. The ASAv is primarily deployed to manage VPN and network switching in cloud or other environments.

Analysis

When command authorization is not enabled, an authenticated remote unprivileged (level 0 or 1) user can change or download the running configuration as well as upload or replace the appliance firmware. Downgrading appliance firmware to an older version would allow an attacker to leverage known vulnerabilities that have been well researched or have publicly available exploit modules.

A simple proof of concept for downloading the running configuration follows:

curl --basic -u notadmin -p -k http://<ip>/admin/system/running-config

The following proof of concept allows an unprivileged user to add a new privileged user to the running configuration:

curl --basic -u notadmin -p -k -X “POST” --data-binary “username fourthuser password backdoor privilege 15” “http://<ip>/admin/config”

According to Cisco “This vulnerability affects Cisco ASA Software that is running on any Cisco product that has web management access enabled.”

Vendor response

Cisco released an advisory, “Cisco Adaptive Security Appliance Software Privilege Escalation Vulnerability,” with details on the vulnerability and patch information. Customers can download the update here.

Solution

Cisco has released an advisory and patches. You can find full details linked below. Cisco also notes “for the fix to be effective, customers who have web management access enabled must ensure that the AAA configuration is accurate and complete. In particular, the aaa authentication http console {LOCAL | <aaa-server>} command must be present.”

Additional information

• Advisory: Cisco Adaptive Security Appliance Software Privilege Escalation Vulnerability
• Tenable Advisory

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