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CVE-2024-20481

KEVmass

Unauthenticated Remote Access VPN DoS in Cisco ASA and FTD Software

CISA: Cisco ASA and FTD Denial-of-Service Vulnerability

CVSS 3.1
5.8 medium
EPSS
16%p97
Published
()
KEV added
AI analysis

CVE-2024-20481 is a denial-of-service vulnerability in the Remote Access VPN (RAVPN) service of Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software, caused by resource exhaustion (CWE-772). An unauthenticated, remote attacker can trigger it by sending a large number of VPN authentication requests to an affected device, consistent with the large-scale VPN brute-force activity Cisco Talos has documented. A successful attack exhausts device resources and causes a denial of service of the RAVPN service, potentially requiring a device reload to restore VPN service, though non-VPN functionality is unaffected. Only ASA and FTD devices with the RAVPN service enabled are affected. The flaw is under active exploitation: CISA added it to the Known Exploited Vulnerabilities catalog on 2024-10-24, and trade press reports Cisco issued urgent fixes for this actively exploited bug.

What to do: Apply the fixed ASA/FTD Software releases specified in Cisco's advisory for CVE-2024-20481, or apply Cisco's documented mitigations (such as rate-limiting/throttling VPN authentication attempts) if patching is not immediately possible. Check RAVPN devices for bursts of failed or unusual VPN authentication requests consistent with brute-forcing, and restrict or disable internet-exposed RAVPN where it is not needed. Per CISA KEV guidance, apply vendor mitigations or discontinue use of the product if mitigations are unavailable.

Affected
Cisco Adaptive Security Appliance (ASA) Software—
Cisco Firepower Threat Defense (FTD) Software—
Estimated exposure
masshundreds of thousands of internet-exposed Cisco ASA/FTD appliances, of which the RAVPN-enabled subset is directly vulnerable — Cisco ASA/FTD firewalls are among the most widely deployed enterprise edge and VPN appliances, and public internet scans (e.g., Shodan/Censys) routinely surface on the order of 100,000+ exposed Cisco ASA/AnyConnect VPN endpoints, so only…

Order-of-magnitude estimate by the model from install counts, market share and public scan data it knows; verify before quoting.

Description

A vulnerability in the Remote Access VPN (RAVPN) service of Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause a denial of service (DoS) of the RAVPN service. This vulnerability is due to resource exhaustion. An attacker could exploit this vulnerability by sending a large number of VPN authentication requests to an affected device. A successful exploit could allow the attacker to exhaust resources, resulting in a DoS of the RAVPN service on the affected device. Depending on the impact of the attack, a reload of the device may be required to restore the RAVPN service. Services that are not related to VPN are not affected. Cisco Talos discussed these attacks in the blog post Large-scale brute-force activity targeting VPNs, SSH services with commonly used login credentials.

CISA Known Exploited Vulnerability
Affected
Cisco Adaptive Security Appliance (ASA) and Firepower Threat Defense (FTD)
Required action
Apply mitigations per vendor instructions or discontinue use of the product if mitigations are unavailable.
Due date
Ransomware use
Unknown
Vendors
cisco
Products
secure firewall threat defense, adaptive security appliance software
Weakness
CWE-772
Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:L
NVD CVE.org CISA KEV GitHub PoCs EPSS (15.8%)

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