# CVE-2021-45955: Memory corruption in n/a

> Heap-based buffer overflow in Dnsmasq allows attackers to execute arbitrary code or cause denial of service via crafted packets.

- **Severity:** Critical 9.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/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:** 31 Dec 2021
- **Updated:** 4 Aug 2024
- **Also known as:** AZL-8962, GHSA-p5g5-mjp3-mr9m

## What is CVE-2021-45955?

CVE-2021-45955 is a critical memory corruption vulnerability in n/a, published on 31 Dec 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Dnsmasq 2.86 has a heap-based buffer overflow in resize_packet (called from FuzzResizePacket and fuzz_rfc1035.c) because of the lack of a proper bounds check upon pseudo header re-insertion. NOTE: the vendor's position is that CVE-2021-45951 through CVE-2021-45957 "do not represent real vulnerabilities, to the best of our knowledge." However, a contributor states that a security patch (mentioned in 016162.html) is needed

Weakness: CWE-787 (Out-of-bounds Write)

## Which versions are affected by CVE-2021-45955?

It affects 1 product.


Products: Thekelleys Dnsmasq.

## How do I fix CVE-2021-45955?

Apply the vendor's patch.

## Is CVE-2021-45955 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2021-45955 exists.

## Other vulnerabilities in n/a

- [CVE-2021-45951](https://insights.sbomify.com/CVE-2021-45951/): Memory corruption in n/a (critical 9.8)
- [CVE-2021-45952](https://insights.sbomify.com/CVE-2021-45952/): Memory corruption in n/a (critical 9.8)
- [CVE-2021-45953](https://insights.sbomify.com/CVE-2021-45953/): Memory corruption in n/a (critical 9.8)
- [CVE-2021-45954](https://insights.sbomify.com/CVE-2021-45954/): Memory corruption in n/a (critical 9.8)
- [CVE-2021-45956](https://insights.sbomify.com/CVE-2021-45956/): Memory corruption in n/a (critical 9.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-45955 and fix it if it is affected.

What it is: CVE-2021-45955 is a critical memory corruption vulnerability in n/a, published on 31 Dec 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2021-45955 exists.

Affected product: n/a. 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-2021-45955/ (Markdown: https://insights.sbomify.com/CVE-2021-45955/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-45955
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-45955
- OSV: https://osv.dev/vulnerability/CVE-2021-45955

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-45955/
Summaries are generated and may contain mistakes; the official description above is the record.