CVE-2020-3191: Cisco Adaptive Security Appliance Software

High severity, CVSS 8.6. EPSS: 1.9% chance of exploitation in the next 30 days.

A vulnerability in DNS over IPv6 packet processing for Cisco Adaptive Security Appliance (ASA) Software and Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause the device to unexpectedly reload, resulting in a denial of service (DoS) condition. The vulnerability is due to improper length validation of a field in an IPv6 DNS packet. An attacker could exploit this vulnerability by sending a crafted DNS query over IPv6, which traverses the affected device. An exploit could allow the attacker to cause the device to reload, resulting in a DoS condition. This vulnerability is specific to DNS over IPv6 traffic only.

Affected products

Cisco Adaptive Security Appliance Software: from 9.6, before 9.6.4.36 (fixed in 9.6.4.36); from 9.8, before 9.8.4.12 (fixed in 9.8.4.12); from 9.9, before 9.9.2.66 (fixed in 9.9.2.66); from 9.10, before 9.10.1.37 (fixed in 9.10.1.37); from 9.12, before 9.12.2.9 (fixed in 9.12.2.9)
Cisco ASA 5505 Firmware: version 9.4(1) only; version 96.4(0.42) only
Cisco ASA 5510 Firmware: version 9.4(1) only; version 96.4(0.42) only
Cisco ASA 5512-X Firmware: version 9.4(1) only; version 96.4(0.42) only
Cisco ASA 5515-X Firmware: version 9.4(1) only; version 96.4(0.42) only
Cisco ASA 5520 Firmware: version 9.4(1) only; version 96.4(0.42) only
Cisco ASA 5525-X Firmware: version 9.4(1) only; version 96.4(0.42) only
Cisco ASA 5540 Firmware: version 9.4(1) only; version 96.4(0.42) only
Cisco ASA 5545-X Firmware: version 9.4(1) only; version 96.4(0.42) only
Cisco ASA 5550 Firmware: version 9.4(1) only; version 96.4(0.42) only
Cisco ASA 5555-X Firmware: version 9.4(1) only; version 96.4(0.42) only
Cisco ASA 5580 Firmware: version 9.4(1) only; version 96.4(0.42) only
Cisco ASA 5585-X Firmware: version 9.4(1) only; version 96.4(0.42) only
Cisco Secure Firewall Threat Defense: from 6.2.3, before 6.2.3.16 (fixed in 6.2.3.16); from 6.3.0, before 6.3.0.6 (fixed in 6.3.0.6); from 6.4.0, before 6.4.0.6 (fixed in 6.4.0.6)

Published 2020-05-06. Last modified 2026-08-11.