# CVE-2020-3191: Denial of service in Cisco Adaptive Security Appliance (ASA) Software

> Remote attackers can cause Cisco ASA and FTD devices to reload via crafted IPv6 DNS packets, resulting in a denial of service.

- **Severity:** High 8.6 (`CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 6 May 2020
- **Updated:** 15 Nov 2024
- **Also known as:** GHSA-54hx-xv6r-c55r

## What is CVE-2020-3191?

CVE-2020-3191 is a high-severity denial of service vulnerability in Cisco Adaptive Security Appliance Software, published on 6 May 2020. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official 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.

Weakness: CWE-20 (Improper Input Validation)

## Which versions are affected by CVE-2020-3191?

It affects 14 products.


Products: Cisco Adaptive Security Appliance Software, Cisco Asa 5505 Firmware, Cisco Asa 5510 Firmware, Cisco Asa 5512-X Firmware, Cisco Asa 5515-X Firmware, Cisco Asa 5520 Firmware, Cisco Asa 5525-X Firmware, Cisco Asa 5540 Firmware, Cisco Asa 5545-X Firmware, Cisco Asa 5550 Firmware, Cisco Asa 5555-X Firmware, Cisco Asa 5580 Firmware, Cisco Asa 5585-X Firmware, Cisco Secure Firewall Threat Defense.

## How do I fix CVE-2020-3191?

No fix has been published for CVE-2020-3191 yet. Limit exposure of the affected software until one is available.

## Is CVE-2020-3191 being exploited?

There is no known exploitation of CVE-2020-3191 in the wild and no public exploit code.

## Other vulnerabilities in Cisco Adaptive Security Appliance Software

- [CVE-2025-20333](https://insights.sbomify.com/CVE-2025-20333/): Cisco Secure Firewall Adaptive Security Appliance (ASA) and Secure Firewall Threat Defense (FTD) Buffer Overflow (critical 9.9, exploited in the wild)
- [CVE-2016-6366](https://insights.sbomify.com/CVE-2016-6366/): Cisco Adaptive Security Appliance (ASA) SNMP Buffer Overflow (high 8.8, exploited in the wild)
- [CVE-2026-20349](https://insights.sbomify.com/CVE-2026-20349/): Cisco Secure Firewall Adaptive Security Appliance (ASA) and Secure Firewall Threat Defense (FTD) Heap Inspection (high 8.6, exploited in the wild)
- [CVE-2024-20353](https://insights.sbomify.com/CVE-2024-20353/): Cisco ASA and FTD Denial of Service (high 8.6, exploited in the wild)
- [CVE-2016-6367](https://insights.sbomify.com/CVE-2016-6367/): Cisco Adaptive Security Appliance (ASA) CLI Remote Code Execution (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2020-3191 and fix it if it is affected.

What it is: CVE-2020-3191 is a high-severity denial of service vulnerability in Cisco Adaptive Security Appliance Software, published on 6 May 2020. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2020-3191 in the wild and no public exploit code.

Affected product: Cisco Adaptive Security Appliance Software. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2020-3191/ (Markdown: https://insights.sbomify.com/CVE-2020-3191/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2020-3191
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2020-3191
- OSV: https://osv.dev/vulnerability/CVE-2020-3191

---
From sbomify Insights: https://insights.sbomify.com/CVE-2020-3191/
Summaries are generated and may contain mistakes; the official description above is the record.