CVE-2016-6367: Cisco Adaptive Security Appliance (ASA) CLI Remote Code Execution Vulnerability

CVE-2016-6367 is a vulnerability in the command-line interface (CLI) parser of Cisco Adaptive Security Appliance (ASA) software. An authenticated local attacker could abuse it to cause a denial-of-service condition or potentially execute code on the device. Because ASA appliances commonly sit at network boundaries and enforce security policy, compromise of the CLI can undermine the integrity of the firewall itself and the networks it protects. Specifics such as exact affected releases must be confirmed against the vendor advisory.

How it works

This issue is classified as CWE-77 (command injection). In products that expose a CLI, the parser is responsible for interpreting administrator-supplied commands and arguments. When input is not adequately validated or sanitized before it is passed to underlying system functions, an attacker who already has authenticated local access can craft input that the parser mishandles.

According to the CISA summary, successful abuse can produce a denial-of-service condition or potentially allow code execution. The attack requires an authenticated local presence; it is not described as unauthenticated remote exploitation. Exact injection vectors, payloads, or privilege-escalation paths are not detailed in the provided facts and should not be assumed—consult the vendor advisory for the precise technical description.

Am I affected? How to find it in your systems

Cisco ASA software runs on dedicated security appliances and virtual instances that provide firewall, VPN, and related perimeter services. These devices are typically managed via console, SSH, or other administrative channels that expose the CLI.

• Inventory all Cisco ASA appliances and virtual ASAs in your environment, including those in HA pairs, DMZs, and remote sites.
• Record the running software version and any feature licenses or configurations that enable CLI access for local or remote administrators.
• Compare each version and configuration against the fixed releases listed in the Cisco advisory for CVE-2016-6367; do not rely on generic version ranges.
• Review administrative access logs and AAA records for unusual CLI sessions, unexpected command sequences, or authentication from atypical sources.
• Watch for unexplained device reloads, process crashes, or CLI parser errors that could indicate attempted abuse, keeping in mind that such symptoms are not unique to this CVE.

If your asset-management or configuration-management database does not already track ASA software levels, prioritize a targeted discovery scan or direct CLI/show-version collection.

How to remediate

The primary remediation is to apply the updates Cisco released for this vulnerability, following the vendor’s instructions exactly. CISA’s required action is to apply updates per vendor instructions.

• Identify the correct fixed software train for each ASA platform and hardware model from the official advisory.
• Schedule maintenance windows that account for reload requirements and high-availability failover testing.
• After patching, verify the new version is active and that CLI functionality and security policies remain intact.
• Restrict CLI access to the minimum set of authenticated administrators, enforce strong authentication (preferably multi-factor where supported), and disable unused management interfaces or protocols.
• Ensure configuration backups and change-control records are current so you can detect unauthorized modifications.

Hardening steps that reduce exposure for CLI-related weaknesses in general—least-privilege admin accounts, command authorization, and session logging—should be applied consistently once the patch is in place.

If you can't patch immediately

When immediate patching is not feasible, reduce risk with compensating controls while you prepare the update.

• Segment management access so that only dedicated jump hosts or management networks can reach the ASA CLI; block broader internal or external reachability.
• Temporarily disable or tightly restrict local accounts and non-essential remote management methods if operationally acceptable.
• Increase monitoring of authentication events, CLI command history, and device health (CPU, memory, unexpected reloads) and alert on anomalies.
• If a web application firewall or network IPS is in the path of management traffic, evaluate whether vendor-supplied signatures or custom rules can provide temporary virtual patching; confirm any such controls against Cisco guidance rather than assuming coverage.
• Document the exception, set a firm patch deadline, and limit the duration of any workaround.

These measures do not eliminate the vulnerability; they only lower the likelihood of successful abuse until the vendor update is applied.

If your data may have been exposed

Actively exploited vulnerabilities on perimeter devices can lead to broader network compromise and data exposure. Known ransomware use of this CVE is not documented in the provided facts. If you suspect the device was abused, follow your incident-response process: isolate affected systems, preserve logs, and assess whether credentials or traffic traversing the ASA could have been at risk. You can also run a free exposure scan of your email addresses to check whether they appear in known breach data sets.