CVE-2023-20269: Mitigating Unauthorized Access in Cisco ASA and Firepower Threat Defense VPNs
Cisco Adaptive Security Appliance and Firepower Threat Defense contain an unauthorized access vulnerability that could allow an unauthenticated, remote attacker to conduct a brute force attack in an attempt to identify valid username and password combinations or establish a clientless SSL VPN session with an unauthorized user.
FREQUENTLY ASKED
What is CVE-2023-20269 and why does it matter?
CVE-2023-20269 is an unauthorized access vulnerability in the remote access VPN feature of Cisco ASA and FTD software. It allows attackers to perform brute force attacks to identify valid credentials or establish unauthorized clientless SSL VPN sessions. It matters because it is actively being exploited in the wild, potentially leading to unauthorized network entry and subsequent ransomware deployment.
Which versions of Cisco ASA and FTD are affected?
A wide range of versions are affected, including Cisco ASA software releases 9.8 through 9.19 and Cisco FTD software releases 6.2.3 through 7.4.0. Specific sub-versions like 9.12.4, 9.16.4, and 7.2.5 are explicitly listed in the advisory. Administrators should check their specific build against the vendor's comprehensive list to determine exposure.
Has a patch been released for this vulnerability?
Cisco has committed to releasing software updates to address this vulnerability. In the interim, critical workarounds such as implementing 'group-lock' to specific profiles and restricting 'vpn-simultaneous-logins' are recommended. These mitigations prevent attackers from using default connection profiles to gain unauthorized access even if they possess valid credentials.
What is the remediation deadline for CVE-2023-20269?
The remediation deadline is October 4, 2023. This date is critical for compliance with CISA's Known Exploited Vulnerabilities (KEV) catalog. For federal agencies and organizations following CISA guidelines, this means patches or vendor-approved mitigations must be applied by this date to reduce the risk of active exploitation by malicious actors.
How can I check if my Cisco deployment is affected?
Organizations can check their status by verifying the software version running on their ASA or FTD devices and confirming if the Remote Access VPN feature is enabled. Furthermore, administrators should audit their connection profiles (tunnel groups) to see if default profiles are accessible and ensure that Multi-Factor Authentication (MFA) is correctly enforced across all VPN entry points.
CVE-2023-20269 identifies a medium-severity unauthorized access vulnerability in Cisco Adaptive Security Appliance (ASA) and Firepower Threat Defense (FTD) software, specifically within the remote access VPN feature. With a CVSS score of 5.0 and evidence of active exploitation, organizations must remediate this flaw by October 4, 2023, to prevent brute force attacks and unauthorized clientless SSL VPN sessions.
Vulnerability Profile
Field
Details
CVE ID
CVE-2023-20269
Affected Product & Versions
Cisco ASA (9.8.1 to 9.19.1.18) and FTD (6.2.3 to 7.4.0)
CVSS Score & Severity
5.0 (MEDIUM)
CVSS Version
3.1
CVSS Vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:L/A:N
Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
LOW
User Interaction
NONE
CWE IDs
CWE-288 (Authentication Bypass Using an Alternate Path or Channel)
Date Disclosed
2023-09-13
Remediation Deadline
2023-10-04
SSVC Exploitation status
Active
Known Ransomware Use
Yes
EPSS Score & Percentile
0.00824 (74.5%)
Patch Available
Yes
Technical Deep Dive: Understanding the AAA Separation Flaw
At the core of CVE-2023-20269 lies CWE-288: Authentication Bypass Using an Alternate Path or Channel. In the context of Cisco ASA and FTD, this manifests as an improper separation of Authentication, Authorization, and Accounting (AAA) services. Specifically, the software fails to strictly isolate AAA functions between the remote access VPN feature, the HTTPS management interface, and site-to-site VPN features.
In a standard secure configuration, different access methods should be confined to their respective connection profiles (also known as tunnel groups). However, this vulnerability allows an attacker to interact with the default connection profile. Because the system does not properly validate which AAA channel is appropriate for a given request, an attacker can use the default tunnel group as an "alternate path" to bypass intended access controls.
The Attack Chain
Reconnaissance/Brute Force: An unauthenticated remote attacker targets the VPN endpoint. They use automated tools to brute force the default connection profile. Because of the AAA overlap, the device responds to these requests, allowing the attacker to verify valid username and password combinations.
Session Establishment: Once valid credentials are identified (or if the attacker already possesses them), they can attempt to establish a clientless SSL VPN session.
Constraint Limitations: It is important to note that a full client-based remote access VPN tunnel (AnyConnect) cannot be established through this exploit. This is because default connection profiles do not have assigned IP address pools, which are required for full tunnel connectivity. However, clientless SSL VPN access remains a significant risk for ASA releases 9.16 and earlier.
Attack Surface and Blast Radius
The attack surface includes any Cisco ASA or FTD device with Remote Access VPN enabled and exposed to the public internet. The blast radius is categorized as "Partial" technical impact. While it does not grant full administrative control or bypass multi-factor authentication (MFA), it provides a foothold for attackers to validate credentials. These credentials can then be leveraged for more sophisticated attacks, lateral movement, or ransomware deployment—a trend observed in recent campaigns targeting Cisco infrastructure.
Who Is Affected: Impact Assessment
Organizations utilizing Cisco ASA or FTD for remote workforce connectivity are the primary targets. The vulnerability affects a massive range of software versions, from legacy 9.8.x ASA builds to modern 7.4.0 FTD releases.
CISA BOD 22-01 Compliance: Due to active exploitation, CISA has added CVE-2023-20269 to the Known Exploited Vulnerabilities (KEV) catalog. Federal Civilian Executive Branch (FCEB) agencies are required to remediate this vulnerability by the October 4, 2023 deadline. Private sector organizations are strongly encouraged to adhere to this same timeline to mitigate the risk of ransomware groups who frequently exploit such flaws to gain initial access.
Official Remediation Steps and Workarounds
Cisco has provided a path for remediation through software updates and configuration-based workarounds. Organizations should prioritize upgrading to fixed software versions as specified in the official Cisco Security Advisory.
Implementation of Workarounds
If immediate patching is not possible, the following mitigations should be applied:
Group-Lock Enforcement: Configure the group-lock command within your VPN profiles to ensure that users are restricted to their authorized tunnel groups. This prevents them from authenticating via the default profile.
Disable Default Profiles: Where possible, redirect all legitimate traffic to custom connection profiles and ensure the default DefaultWEBVPNGroup and DefaultRAGroup are restricted.
Restrict Simultaneous Logins: Set vpn-simultaneous-logins to zero for default profiles to prevent them from being used for active sessions.
Audit Local Databases: If using local AAA, ensure that no sensitive accounts are stored locally without strict MFA enforcement.
Security Best Practices for VPN Hardening
To address CWE-288 and general VPN risks, implement the following defensive measures:
Enforce Multi-Factor Authentication (MFA): Ensure that MFA is required for all VPN connections. This vulnerability does not bypass MFA; therefore, a robust second factor remains the strongest defense against brute-forced credentials.
Log and Monitor AAA Failures: Set up alerting for excessive authentication failures on default tunnel groups. High volumes of failed attempts are a primary indicator of brute-force activity related to this CVE.
Geofencing and IP Whitelisting: If your workforce is geographically concentrated, restrict VPN access to known IP ranges or countries to reduce the reachable attack surface.
Use Client Certificates: Transition from password-based authentication to certificate-based authentication (AnyConnect Certificate-only or Double Authentication) to eliminate the risk of credential brute-forcing.
Regular Configuration Audits: Use automated tools to audit Cisco ASA/FTD configurations for the presence of default tunnel groups and unassigned IP pools.
Implement Endpoint Posture Checks: Ensure that only managed devices with up-to-date security software can establish VPN sessions, limiting the utility of stolen credentials used from unmanaged attacker machines.