CVE-202 Exploitation Understanding Impact Detection

Exploiting CVE-2023-20269 targets Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software. This vulnerability is an authorization flaw within the Remote Access VPN (RA VPN) feature. It allows an unauthenticated, remote attacker to conduct brute-force attacks against valid username and password combinations. An authenticated attacker running Cisco ASA Software Release 9.16 or earlier can also establish a clientless SSL VPN session with an unauthorized user. The National Vulnerability Database (NVD) assigned CVE-2023-20269 a CVSSv3.1 Base Score of 5.0 (Medium) with a vector string of CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:L/A:N. However, other sources indicate a CVSS score of 9.8 (Critical) or note that its impact can be critical depending on network configuration. CISA has added this vulnerability to its Known Exploited Vulnerabilities Catalog, indicating active exploitation in the wild. Ransomware groups, including Akira and LockBit, have actively leveraged this vulnerability.

Vulnerability and Impact

CVE-2023-20269 is an authorization vulnerability. It affects the remote access VPN feature of Cisco ASA Software and Cisco FTD Software. Specifically, it stems from improper separation of Authentication, Authorization, and Accounting (AAA) between the remote access VPN feature and the HTTPS management and site-to-site VPN features. This flaw does not bypass authentication directly. Instead, it facilitates credential brute-force attacks. Affected products include Cisco Adaptive Security Appliance (ASA) Software versions 9.8.x through 9.19.x and Cisco Firepower Threat Defense (FTD) Software versions 6.2.3 through 7.4.0. Cisco ASA Software Release 9.16 or earlier is additionally vulnerable to unauthorized clientless SSL VPN session establishment by an authenticated attacker. Successfully exploiting CVE-2023-20269 allows attackers to identify valid VPN credentials at scale. This leads to unauthorized VPN session establishment and potential lateral movement within corporate networks. This poses significant risks to data confidentiality, integrity, and availability.

Technical Root Cause Analysis

The root cause of CVE-2023-20269 lies in the incomplete isolation of AAA functions across different VPN contexts. The remote access VPN feature shares AAA logic with HTTPS management and site-to-site VPN features. When an attacker specifies a default connection profile or tunnel group, the AAA subsystem processes authentication requests. It does this without strictly enforcing the boundaries intended for these separate feature contexts. This expands the attack surface for credential validation. In older releases, it also expands the attack surface for session establishment. The vulnerability is classified under CWE-288 (Authentication Bypass Using an Alternate Path or Channel) and CWE-863 (Incorrect Authorization). This improper separation allows attackers to interact with AAA functions that should be restricted to administrative or site-to-site contexts. This design flaw enables brute-force attacks against user credentials. It bypasses typical rate-limiting or blocking mechanisms.

Exploitation Mechanics

Exploiting CVE-2023-20269 involves an unauthenticated remote attacker sending authentication requests to the VPN endpoint. The attacker specifies a default connection profile or tunnel group (e.g., DefaultRAGroup, DefaultWEBVPNGroup, DefaultADMINGroup, DefaultL2LGroup). This process allows credentials to be tested rapidly. It enables automated enumeration of valid usernames and passwords against the appliance. Threat actors use this technique for initial access, especially when multi-factor authentication (MFA) is not enforced. For brute-force attacks to succeed, at least one user must have a password configured in the local database or the HTTPS management authentication must point to a valid AAA server. Additionally, either SSL VPN or IKEv2 VPN must be enabled on at least one interface. For establishing a clientless SSL VPN session with an unauthorized user (applicable to Cisco ASA Software Release 9.16 or earlier), additional conditions are required. The attacker needs valid credentials for a user in the LOCAL database or the AAA server used for HTTPS management authentication. SSL VPN must be enabled on at least one interface, and the clientless SSL VPN protocol must be allowed in the `DfltGrpPolicy`. Client-based remote access VPN tunnels cannot be established through these default connection profiles because they lack an IP address pool. The vulnerability itself does not bypass authentication; valid credentials, including MFA if configured, remain necessary to establish a VPN session.

Detection

Detecting attempts to exploit CVE-2023-20269 requires vigilant monitoring of network and system logs. Examine VPN authentication logs for unauthorized access attempts or anomalous patterns. Look for authentication failures originating from a small set of source IP addresses targeting many usernames, or many source IPs targeting a small set of usernames (password spraying patterns). Successful clientless SSL VPN session establishment from unusual geographic locations or hosting provider ranges also indicates compromise. Monitor for subsequent post-VPN activity consistent with ransomware affiliate tradecraft, such as reconnaissance and lateral movement from VPN-assigned IP ranges. Implement custom detection rules within your Security Information and Event Management (SIEM) system. These rules can include packet inspection or behavioral monitoring for signs of exploitation. Ensure endpoint and threat detection tools identify unauthorized code execution or privilege escalation events. Use tools like a free port scanner to identify exposed VPN services on your external attack surface. Secably's attack surface management capabilities can help continuously monitor for exposed services and potential misconfigurations that attackers might target.

Remediation Steps

Immediate remediation for CVE-2023-20269 involves applying the fixed Cisco ASA and FTD software releases. Consult the Cisco Security Advisory cisco-sa-asaftd-ravpn-auth-8LyfCkeC for specific patch information. Until patches are available, implement the following workarounds:

• Enforce multi-factor authentication (MFA) on all remote access VPN accounts. This prevents credential discovery from resulting in a usable session.
• Audit default connection profiles and tunnel groups (e.g., DefaultRAGroup, DefaultWEBVPNGroup, DefaultADMINGroup, DefaultL2LGroup). Restrict their use through AAA configuration.
• Deny access with Default Group Policy by setting `vpn-simultaneous-logins` for `DfltGrpPolicy` to zero. Ensure all VPN session profiles point to a custom policy.
• Implement local user database restrictions. Lock specific users to a single profile using the `group-lock` option.
• Secure Default Remote Access VPN profiles. Point all non-default profiles to a sinkhole AAA server (dummy LDAP server) and enable logging.
• Restrict VPN access to trusted networks where possible.

Cisco recommends enabling logging to a remote syslog server for improved correlation and auditing.

Timeline of Disclosure

Cisco initially published the advisory for CVE-2023-20269 on September 6, 2023. This followed internal identification and extensive analysis. Rapid7 reported attempted exploitation of this vulnerability to Cisco. Cisco confirmed awareness of active exploitation in the wild by ransomware groups, including Akira, at the time of disclosure. CISA added CVE-2023-20269 to its Known Exploited Vulnerabilities Catalog shortly after its disclosure. The NVD last updated the CVE entry on October 28, 2025. While no public proof-of-concept code was referenced in the advisory, the vulnerability has been actively exploited.