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Vulnerability record · CVE-2020-3191 · published 6 May 2020

CVE-2020-3191: Cisco secure firewall threat defense improper input validation vulnerability

Cisco · Secure Firewall Threat Defense

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.

8.6 CVSS 3.1 High EPSS 1.9% · top 21.6% CWE-20 · Improper input validation
8.6CVSS 3.1 base score, v2 5.0
1.9%EPSS exploitation probability, 30 days
NoNot in CISA KEV
14Affected product versions listed by NVD
2References
11 Aug 2026Last modified by NVD

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.

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H

Affected products

14 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asaftd-ipv6-67pA658k Vendor Advisory
https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asaftd-ipv6-67pA658k Vendor Advisory

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Same products first, then exploited flaws of the same weakness class.

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Source: NIST National Vulnerability Database (record CVE-2020-3191), CISA KEV, FIRST EPSS (scores of 2026-09-27). This page is refreshed as NVD updates the record.