CVE-2022-20759: Cisco Firepower Threat Defense Escalation

CVE-2022-20759 Overview

A vulnerability exists in the web services interface for remote access VPN features of Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software that could allow an authenticated, but unprivileged, remote attacker to elevate privileges to level 15. This privilege escalation vulnerability stems from improper separation of authentication and authorization scopes within the affected devices.

An attacker could exploit this vulnerability by sending crafted HTTPS messages to the web services interface of an affected device. A successful exploit could allow the attacker to gain privilege level 15 access to the web management interface, which is the highest administrative privilege level on Cisco devices. This includes full access using management tools like Cisco Adaptive Security Device Manager (ASDM) or Cisco Security Manager (CSM).

Critical Impact

Authenticated attackers can escalate to level 15 administrative privileges on Cisco ASA devices, gaining complete control over the web management interface and associated management tools.

Affected Products

• Cisco Adaptive Security Appliance (ASA) Software
• Cisco Firepower Threat Defense (FTD) Software
• Cisco Firepower Threat Defense version 7.1.0

Discovery Timeline

• May 3, 2022 - CVE-2022-20759 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2022-20759

Vulnerability Analysis

This vulnerability falls under the category of Privilege Escalation and is classified under CWE-266 (Incorrect Privilege Assignment) and CWE-269 (Improper Privilege Management). The root issue lies in how the web services interface handles the separation between authentication and authorization mechanisms for remote access VPN features.

When a user authenticates to the web services interface, the system fails to properly enforce privilege boundaries. This allows an authenticated user with limited privileges to craft specific HTTPS requests that the system interprets as originating from a highly privileged account. The vulnerability enables vertical privilege escalation, where a low-privileged user can gain administrative (level 15) access.

It's important to note that with Cisco FTD Software specifically, the impact is somewhat reduced because the affected web management interface only allows read access. However, on Cisco ASA Software, full administrative control can be obtained.

Root Cause

The vulnerability is caused by improper separation of authentication and authorization scopes within the web services interface. The affected devices fail to properly validate the privilege level of authenticated users when processing certain HTTPS requests to the web management interface. This authorization bypass allows authenticated users to access functionality reserved for administrators without proper privilege verification.

Attack Vector

The attack is network-based and requires the attacker to first authenticate to the remote access VPN web services interface. Once authenticated with any valid credentials (even low-privilege ones), the attacker can exploit the vulnerability by sending specially crafted HTTPS messages to the web services interface. The attack requires no user interaction and has low complexity, making it relatively straightforward to execute once initial authentication is obtained.

The exploitation involves manipulating HTTPS requests sent to the web services interface to bypass authorization checks. The attacker sends crafted requests that exploit the improper separation between authentication and authorization scopes, effectively tricking the system into granting level 15 privileges. For detailed technical information, refer to the GitHub Security Advisory.

Detection Methods for CVE-2022-20759

Indicators of Compromise

• Unusual privilege level changes in system logs, particularly users being granted level 15 access unexpectedly
• Anomalous HTTPS traffic patterns to the web services interface, especially from previously low-privilege accounts
• Unexpected administrative sessions initiated through ASDM or CSM from user accounts that should not have such access
• Authentication logs showing successful logins followed by immediate administrative actions

Detection Strategies

• Monitor authentication and authorization logs for privilege escalation patterns on ASA and FTD devices
• Implement network monitoring to detect crafted HTTPS requests targeting the web services interface
• Deploy SIEM rules to alert on users accessing administrative interfaces (ASDM, CSM) who are not in the approved administrator group
• Review access logs for any VPN users performing configuration changes or accessing management tools

Monitoring Recommendations

• Enable detailed logging on Cisco ASA and FTD devices to capture all authentication and authorization events
• Configure alerts for any privilege level changes, especially elevations to level 15
• Monitor network traffic for anomalous patterns in HTTPS communications with the web services interface
• Regularly audit user privilege assignments and compare against expected baselines

How to Mitigate CVE-2022-20759

Immediate Actions Required

• Apply the security patches provided by Cisco immediately for all affected ASA and FTD devices
• Review and restrict access to the web services interface to only necessary users and networks
• Audit current user accounts and their privilege levels to ensure no unauthorized escalation has occurred
• Implement network segmentation to limit exposure of the management interface

Patch Information

Cisco has released security updates to address this vulnerability. Administrators should consult the Cisco Security Advisory for specific patch versions and upgrade guidance. It is critical to update to the latest available software versions that contain the fix for this vulnerability.

Workarounds

• Restrict access to the web services interface by implementing strict access control lists (ACLs) that limit connections to trusted IP addresses only
• Disable remote access VPN web services interface if not operationally required
• Implement multi-factor authentication for VPN access to add an additional layer of security
• Consider using out-of-band management networks to isolate administrative interfaces from user traffic

# Example: Restrict management access to specific IP ranges
access-list MGMT-ACL extended permit tcp host 192.168.1.10 any eq https
access-list MGMT-ACL extended deny tcp any any eq https
http 192.168.1.10 255.255.255.255 inside