# CVE-2020-25687: Memory corruption in dnsmasq

> Remote attackers can cause a denial of service in dnsmasq via heap overflow when DNSSEC is enabled.

- **Severity:** Medium 5.9 (`CVSS:3.1/AV:N/AC:H/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:** 20 Jan 2021
- **Updated:** 4 Nov 2025
- **Also known as:** ALPINE-CVE-2020-25687, CLEANSTART-2026-YQ60071, DEBIAN-CVE-2020-25687, GHSA-rv27-69cw-6j7x, UBUNTU-CVE-2020-25687

## What is CVE-2020-25687?

CVE-2020-25687 is a medium-severity memory corruption vulnerability in Debian Debian Linux, published on 20 Jan 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

A flaw was found in dnsmasq before version 2.83. A heap-based buffer overflow was discovered in dnsmasq when DNSSEC is enabled and before it validates the received DNS entries. This flaw allows a remote attacker, who can create valid DNS replies, to cause an overflow in a heap-allocated memory. This flaw is caused by the lack of length checks in rfc1035.c:extract_name(), which could be abused to make the code execute memcpy() with a negative size in sort_rrset() and cause a crash in dnsmasq, resulting in a denial of service. The highest threat from this vulnerability is to system availability.

Weakness: CWE-122 (Heap-based Buffer Overflow)

## Which versions are affected by CVE-2020-25687?

It affects 3 products.


Products: Debian Debian Linux, Fedoraproject Fedora, Thekelleys Dnsmasq.

## How do I fix CVE-2020-25687?

Upgrade to a fixed version.

## Is CVE-2020-25687 being exploited?

There is no known exploitation of CVE-2020-25687 in the wild and no public exploit code.

## Other vulnerabilities in Debian Debian Linux

- [CVE-2015-3306](https://insights.sbomify.com/CVE-2015-3306/): ProFTPD Improper Access Control (critical 10.0, exploited in the wild)
- [CVE-2025-49113](https://insights.sbomify.com/CVE-2025-49113/): RoundCube Webmail Deserialization of Untrusted Data (critical 9.9, exploited in the wild)
- [CVE-2026-24061](https://insights.sbomify.com/CVE-2026-24061/): GNU InetUtils Argument Injection (critical 9.8, exploited in the wild)
- [CVE-2025-39682](https://insights.sbomify.com/CVE-2025-39682/): Linux Kernel Improper Check for Unusual or Exceptional Conditions (critical 9.8, exploited in the wild)
- [CVE-2024-9680](https://insights.sbomify.com/CVE-2024-9680/): Mozilla Firefox Use-After-Free (critical 9.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2020-25687 and fix it if it is affected.

What it is: CVE-2020-25687 is a medium-severity memory corruption vulnerability in Debian Debian Linux, published on 20 Jan 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-2020-25687 in the wild and no public exploit code.

Affected product: Debian Debian 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-2020-25687/ (Markdown: https://insights.sbomify.com/CVE-2020-25687/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2020-25687
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2020-25687
- OSV: https://osv.dev/vulnerability/CVE-2020-25687

---
From sbomify Insights: https://insights.sbomify.com/CVE-2020-25687/
Summaries are generated and may contain mistakes; the official description above is the record.