CVE-2020-3191: Cisco Adaptive Security Appliance Software and Firepower Threat Defense Software IPv6 DNS Denial of Service Vulnerability

Severity: high (CVSS 8.6 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 1.9% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2020-05-06 · updated 2026-08-11
Weakness: CWE-20

Description

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

How to fix

Upgrade to a fixed version: Cisco ASA Software 9.10.1.37, 9.12.2.9, 9.6.4.36, 9.8.4.12; Cisco Firepower Threat Defense Software 6.2.3.16, 6.3.0.6, 6.4.0.6. Check the vendor advisory for mitigations.

References

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