# CVE-2021-25218: Denial of service in BIND9

> Remote attackers can cause a denial of service in BIND DNS servers by triggering an assertion failure when RRL is enabled and UDP fragmentation is required.

- **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:** 18 Aug 2021
- **Updated:** 17 Sep 2024
- **Also known as:** ALPINE-CVE-2021-25218, GHSA-cc8x-chx9-c63q

## What is CVE-2021-25218?

CVE-2021-25218 is a high-severity denial of service vulnerability in Fedoraproject Fedora, published on 18 Aug 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

In BIND 9.16.19, 9.17.16. Also, version 9.16.19-S1 of BIND Supported Preview Edition When a vulnerable version of named receives a query under the circumstances described above, the named process will terminate due to a failed assertion check. The vulnerability affects only BIND 9 releases 9.16.19, 9.17.16, and release 9.16.19-S1 of the BIND Supported Preview Edition.

Weakness: CWE-617 (Reachable Assertion)

## Which versions are affected by CVE-2021-25218?

It affects 2 products.


Products: Fedoraproject Fedora, Isc Bind.

## How do I fix CVE-2021-25218?

Upgrade to a fixed version.

## Is CVE-2021-25218 being exploited?

There is no known exploitation of CVE-2021-25218 in the wild and no public exploit code.

## Other vulnerabilities in Fedoraproject Fedora

- [CVE-2024-4577](https://insights.sbomify.com/CVE-2024-4577/): PHP-CGI OS Command Injection (critical 9.8, exploited in the wild)
- [CVE-2021-39226](https://insights.sbomify.com/CVE-2021-39226/): Grafana Authentication Bypass (critical 9.8, exploited in the wild)
- [CVE-2019-5544](https://insights.sbomify.com/CVE-2019-5544/): VMware ESXi and Horizon DaaS OpenSLP Heap-Based Buffer Overflow (critical 9.8, exploited in the wild)
- [CVE-2024-4947](https://insights.sbomify.com/CVE-2024-4947/): Google Chromium V8 Type Confusion (critical 9.6, exploited in the wild)
- [CVE-2024-4671](https://insights.sbomify.com/CVE-2024-4671/): Google Chromium Visuals Use-After-Free (critical 9.6, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-25218 and fix it if it is affected.

What it is: CVE-2021-25218 is a high-severity denial of service vulnerability in Fedoraproject Fedora, published on 18 Aug 2021. 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-2021-25218 in the wild and no public exploit code.

Affected product: Fedoraproject Fedora. 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-2021-25218/ (Markdown: https://insights.sbomify.com/CVE-2021-25218/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-25218
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-25218
- OSV: https://osv.dev/vulnerability/CVE-2021-25218

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-25218/
Summaries are generated and may contain mistakes; the official description above is the record.