CVE-2020-3259

Think of this like a door in a building’s lobby that shouldn’t show anything inside. With CVE-2020-3259, a stranger who can reach that doorway may be able to “peek into” the building’s memory and pull out confidential information. On Cisco ASA/Firepower devices, this centers on the web services area used by certain AnyConnect/WebVPN setups.

This affects organizations that run Cisco Adaptive Security Appliance (ASA) and/or Firepower Threat Defense software (including the “Secure Firewall Threat Defense” line) when they use the specific AnyConnect and WebVPN configurations tied to this web services interface.

It matters most if the vulnerable web services are reachable from the internet. Because the issue involves an unauthenticated request, you generally don’t need existing user access for it to be relevant—reachability is the gate.

This is urgent (RED) because it is confirmed in CISA’s KEV as being used in ransomware campaigns, not just a theoretical problem. Public exploits are available as well, which lowers the barrier for attackers to attempt it against exposed systems.

If you have the affected AnyConnect/WebVPN web services reachable from outside, treat this as an immediate patching/mitigation priority.

1. Confirm whether you are exposed

• Determine whether your Cisco deployment uses the AnyConnect and WebVPN setup that maps to the vulnerable web services interface described for CVE-2020-3259.
• Check which network paths can reach the relevant web services from the internet (firewall/NAT rules, port exposure, reverse proxies, etc.).

2. Confirm versions

• For each affected appliance/instance, record the exact running version of:
  • Secure Firewall Threat Defense (if applicable)
  • Adaptive Security Appliance (ASA) software (if applicable)

3. Compare against fixed releases (choose the right target)

• If you are on Secure Firewall Threat Defense, upgrade to 6.2.3.16.
• If you are on Adaptive Security Appliance software, upgrade to 9.8.4.20.

4. Upgrade or apply Cisco mitigations

• Preferred: upgrade to the fixed version(s) above.
• If you cannot upgrade quickly, implement Cisco’s mitigations per the Cisco Security Advisory referenced in the provided vendor remediation notes, and document exactly what changed.

5. Post-change verification

• After upgrading/mitigating, re-test that the affected web services/WebVPN/AnyConnect exposure is no longer publicly reachable beyond what your business requires.
• Review logs for abnormal requests to the web services interface and confirm normal operations for AnyConnect/WebVPN users.

6. Timeline guidance

• CISA KEV remediation due date for this item was 2024-03-07. If you are still vulnerable today, prioritize reaching fixed status immediately.

Severity is HIGH (CVE-2020-3259; CVSS 7.5). The confirmed real-world exploitation status comes from CISA KEV inclusion and required action listed by CISA.

Mechanism: a buffer tracking issue occurs while parsing invalid URLs requested from the Cisco web services interface. An unauthenticated attacker can send a crafted GET request to trigger memory disclosure, potentially allowing retrieval of memory contents and confidential information.

Scope note: the impact is tied to specific AnyConnect and WebVPN configurations.

Exploitation posture: CISA KEV confirms KEV listing used in ransomware campaigns; a public exploit is available. EPSS provides predicted likelihood, but for urgency handling, KEV/exploitation status is treated as the decisive signal.