CVE-2023-20269
Description
A vulnerability in the remote access VPN feature of Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to conduct a brute force attack in an attempt to identify valid username and password combinations or an authenticated, remote attacker to establish a clientless SSL VPN session with an unauthorized user.
This vulnerability is due to improper separation of authentication, authorization, and accounting (AAA) between the remote access VPN feature and the HTTPS management and site-to-site VPN features. An attacker could exploit this vulnerability by specifying a default connection profile/tunnel group while conducting a brute force attack or while establishing a clientless SSL VPN session using valid credentials. A successful exploit could allow the attacker to achieve one or both of the following:
Identify valid credentials that could then be used to establish an unauthorized remote access VPN session.
Establish a clientless SSL VPN session (only when running Cisco ASA Software Release 9.16 or earlier).
Notes:
Establishing a client-based remote access VPN tunnel is not possible as these default connection profiles/tunnel groups do not and cannot have an IP address pool configured.
This vulnerability does not allow an attacker to bypass authentication. To successfully establish a remote access VPN session, valid credentials are required, including a valid second factor if multi-factor authentication (MFA) is configured.
Cisco will release software updates that address this vulnerability. There are workarounds that address this vulnerability.
Summary dbcve.org
A vulnerability in Cisco ASA and FTD remote access VPN allows attackers to specify default connection profiles/tunnel groups during authentication attempts. Due to improper AAA separation between remote access VPN and management/site-to-site VPN features, this enables credential harvesting via brute force or unauthorized clientless SSL VPN session establishment (ASA 9.16 and earlier). The attack requires valid credentials but bypasses intended connection profile restrictions.
Mitigation
Implement Cisco-provided workarounds (likely involving VPN connection profile restrictions or access control) and apply available software updates. Until patched, monitor for anomalous VPN authentication patterns targeting default tunnel groups.