# CVE-2020-8621: Attempting QNAME minimization after forwarding can lead to an assertion failure in resolver.c

> An attacker can crash the DNS server by sending specific queries if QNAME minimization and forward first are enabled.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/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:** Yes
- **Published:** 21 Aug 2020
- **Updated:** 16 Sep 2024
- **Also known as:** ALPINE-CVE-2020-8621, DEBIAN-CVE-2020-8621, GHSA-7vc6-qmjj-2j83, UBUNTU-CVE-2020-8621

## What is CVE-2020-8621?

CVE-2020-8621 is a high-severity denial of service vulnerability in Canonical Ubuntu Linux, published on 21 Aug 2020. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

In BIND 9.14.0 -> 9.16.5, 9.17.0 -> 9.17.3, If a server is configured with both QNAME minimization and 'forward first' then an attacker who can send queries to it may be able to trigger the condition that will cause the server to crash. Servers that 'forward only' are not affected.

Weakness: CWE-617 (Reachable Assertion)

## Which versions are affected by CVE-2020-8621?

It affects 5 products.


Products: Canonical Ubuntu Linux, Isc Bind, Netapp Steelstore Cloud Integrated Storage, Opensuse Leap, Synology Dns Server.

## How do I fix CVE-2020-8621?

Upgrade to a fixed version.

## Is CVE-2020-8621 being exploited?

There is no known exploitation of CVE-2020-8621 in the wild and no public exploit code.

## Other vulnerabilities in Canonical Ubuntu Linux

- [CVE-2020-11651](https://insights.sbomify.com/CVE-2020-11651/): SaltStack Salt Authentication Bypass (critical 9.8, exploited in the wild)
- [CVE-2020-7247](https://insights.sbomify.com/CVE-2020-7247/): OpenSMTPD Remote Code Execution (critical 9.8, exploited in the wild)
- [CVE-2019-16928](https://insights.sbomify.com/CVE-2019-16928/): Exim Out-of-bounds Write (critical 9.8, exploited in the wild)
- [CVE-2018-6789](https://insights.sbomify.com/CVE-2018-6789/): Exim Buffer Overflow (critical 9.8, exploited in the wild)
- [CVE-2015-2590](https://insights.sbomify.com/CVE-2015-2590/): Oracle Java SE and Java SE Embedded Remote Code Execution (critical 9.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2020-8621 and fix it if it is affected.

What it is: CVE-2020-8621 is a high-severity denial of service vulnerability in Canonical Ubuntu Linux, published on 21 Aug 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-2020-8621 in the wild and no public exploit code.

Affected product: Canonical Ubuntu Linux. 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-2020-8621/ (Markdown: https://insights.sbomify.com/CVE-2020-8621/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2020-8621
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2020-8621
- OSV: https://osv.dev/vulnerability/CVE-2020-8621

---
From sbomify Insights: https://insights.sbomify.com/CVE-2020-8621/
Summaries are generated and may contain mistakes; the official description above is the record.