How severe is CVE-2020-3191?

CVE-2020-3191 has a CVSS 3.x base score of 8.6, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2020-3191 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (76th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2020-3191?

CVE-2020-3191 primarily affects Cisco Firepower Threat Defense. In total, 26 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2020-3191?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

When was CVE-2020-3191 published?

CVE-2020-3191 was published on 2020-05-06 and last updated on 2026-06-17.

CVE-2020-3191

CVE-2020-3191 is a high-severity vulnerability in Cisco Firepower Threat Defense with a CVSS 3.x base score of 8.6. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-20.

Key facts

Severity: High (CVSS 3.x base score 8.6)
CVSS v2: 5.0
EPSS exploit prediction: 2% (76th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-20
Affected product: Cisco Firepower Threat Defense
Published: 2020-05-06
Last modified: 2026-06-17

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.

Frequently asked questions

What is CVE-2020-3191?: 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.
How severe is CVE-2020-3191?: CVE-2020-3191 has a CVSS 3.x base score of 8.6, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2020-3191 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (76th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2020-3191?: CVE-2020-3191 primarily affects Cisco Firepower Threat Defense. In total, 26 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2020-3191?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2020-3191 published?: CVE-2020-3191 was published on 2020-05-06 and last updated on 2026-06-17.

References

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

Affected products (26)

cpe:2.3:a:cisco:firepower_threat_defense:*:*:*:*:*:*:*:*
cpe:2.3:o:cisco:asa_5505_firmware:9.4\(1\):*:*:*:*:*:*:*
cpe:2.3:o:cisco:asa_5505_firmware:96.4\(0.42\):*:*:*:*:*:*:*
cpe:2.3:o:cisco:asa_5510_firmware:9.4\(1\):*:*:*:*:*:*:*
cpe:2.3:o:cisco:asa_5510_firmware:96.4\(0.42\):*:*:*:*:*:*:*
cpe:2.3:o:cisco:asa_5512-x_firmware:9.4\(1\):*:*:*:*:*:*:*
cpe:2.3:o:cisco:asa_5512-x_firmware:96.4\(0.42\):*:*:*:*:*:*:*
cpe:2.3:o:cisco:asa_5515-x_firmware:9.4\(1\):*:*:*:*:*:*:*
cpe:2.3:o:cisco:asa_5515-x_firmware:96.4\(0.42\):*:*:*:*:*:*:*
cpe:2.3:o:cisco:asa_5520_firmware:9.4\(1\):*:*:*:*:*:*:*
cpe:2.3:o:cisco:asa_5520_firmware:96.4\(0.42\):*:*:*:*:*:*:*
cpe:2.3:o:cisco:asa_5525-x_firmware:9.4\(1\):*:*:*:*:*:*:*
cpe:2.3:o:cisco:asa_5525-x_firmware:96.4\(0.42\):*:*:*:*:*:*:*
cpe:2.3:o:cisco:asa_5540_firmware:9.4\(1\):*:*:*:*:*:*:*
cpe:2.3:o:cisco:asa_5540_firmware:96.4\(0.42\):*:*:*:*:*:*:*
cpe:2.3:o:cisco:asa_5545-x_firmware:9.4\(1\):*:*:*:*:*:*:*
cpe:2.3:o:cisco:asa_5545-x_firmware:96.4\(0.42\):*:*:*:*:*:*:*
cpe:2.3:o:cisco:asa_5550_firmware:9.4\(1\):*:*:*:*:*:*:*
cpe:2.3:o:cisco:asa_5550_firmware:96.4\(0.42\):*:*:*:*:*:*:*
cpe:2.3:o:cisco:asa_5555-x_firmware:9.4\(1\):*:*:*:*:*:*:*
cpe:2.3:o:cisco:asa_5555-x_firmware:96.4\(0.42\):*:*:*:*:*:*:*
cpe:2.3:o:cisco:asa_5580_firmware:9.4\(1\):*:*:*:*:*:*:*
cpe:2.3:o:cisco:asa_5580_firmware:96.4\(0.42\):*:*:*:*:*:*:*
cpe:2.3:o:cisco:asa_5585-x_firmware:9.4\(1\):*:*:*:*:*:*:*
cpe:2.3:o:cisco:asa_5585-x_firmware:96.4\(0.42\):*:*:*:*:*:*:*
cpe:2.3:o:cisco:adaptive_security_appliance_software:*:*:*:*:*:*:*:*

More vulnerabilities in Cisco Firepower Threat Defense

CVE-2021-44228 — Critical (CVSS 10.0): Apache Log4j2 2.0-beta9 through 2.15.0 (excluding security releases 2.12.2, 2.12.3, and 2.3.1) JNDI features used in…
CVE-2018-0101 — Critical (CVSS 10.0): A vulnerability in the Secure Sockets Layer (SSL) VPN functionality of the Cisco Adaptive Security Appliance (ASA)…
CVE-2025-20333 — Critical (CVSS 9.9): A vulnerability in the VPN web server of Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Cisco…
CVE-2024-20412 — Critical (CVSS 9.3): A vulnerability in Cisco Firepower Threat Defense (FTD) Software for Cisco Firepower 1000, 2100, 3100, and 4200 Series…
CVE-2020-3187 — Critical (CVSS 9.1): A vulnerability in the web services interface of Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower…
CVE-2025-20363 — Critical (CVSS 9.0): A vulnerability in the web services of Cisco Secure Firewall Adaptive Security Appliance (ASA) Software, Cisco Secure…

All CVEs affecting Cisco Firepower Threat Defense →

Other CWE-20 (Improper Input Validation) vulnerabilities

CVE-2026-48316 — Critical (CVSS 10.0): ColdFusion versions 2025.9, 2023.20 and earlier are affected by an Improper Input Validation vulnerability that could…
CVE-2026-48281 — Critical (CVSS 10.0): ColdFusion versions 2025.9, 2023.20 and earlier are affected by an Improper Input Validation vulnerability that could…
CVE-2026-48277 — Critical (CVSS 10.0): ColdFusion versions 2025.9, 2023.20 and earlier are affected by an Improper Input Validation vulnerability that could…
CVE-2026-48055 — Critical (CVSS 10.0): Streambert is a cross-platform Electron Desktop App to stream and download any video media. In versions 2.4.0 and…
CVE-2026-34910 — Critical (CVSS 10.0): A malicious actor with access to the network could exploit an Improper Input Validation vulnerability found in UniFi OS…
CVE-2026-33587 — Critical (CVSS 10.0): Lack of user input sanitisation in Open Notebook v1.8.3 allows the application user to execute Python code (and…

Browse all CWE-20 (Improper Input Validation) vulnerabilities →