# CVE-2021-36159: Memory corruption in n/a

> An out-of-bounds read in libfetch's FTP passive mode parsing allows attackers to cause denial of service or disclose memory contents.

- **Severity:** Critical 9.1 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/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:** 3 Aug 2021
- **Updated:** 4 Aug 2024
- **Also known as:** ALPINE-CVE-2021-36159, CLEANSTART-2024-QY49734, GHSA-cqp5-89fm-vp89

## What is CVE-2021-36159?

CVE-2021-36159 is a critical memory corruption vulnerability in n/a, published on 3 Aug 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

libfetch before 2021-07-26, as used in apk-tools, xbps, and other products, mishandles numeric strings for the FTP and HTTP protocols. The FTP passive mode implementation allows an out-of-bounds read because strtol is used to parse the relevant numbers into address bytes. It does not check if the line ends prematurely. If it does, the for-loop condition checks for the '\0' terminator one byte too late.

Weakness: CWE-125 (Out-of-bounds Read)

## Which versions are affected by CVE-2021-36159?

It affects 1 product.


Products: Freebsd Libfetch.

## How do I fix CVE-2021-36159?

Upgrade to a fixed version.

## Is CVE-2021-36159 being exploited?

There is no known exploitation of CVE-2021-36159 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-36159 and fix it if it is affected.

What it is: CVE-2021-36159 is a critical memory corruption vulnerability in n/a, published on 3 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-2021-36159 in the wild and no public exploit code.

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-2021-36159/ (Markdown: https://insights.sbomify.com/CVE-2021-36159/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-36159
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-36159
- OSV: https://osv.dev/vulnerability/CVE-2021-36159

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-36159/
Summaries are generated and may contain mistakes; the official description above is the record.