# CVE-2021-20285: Memory corruption in upx

> Attackers can cause a denial of service via a crafted ELF file processed by the UPX executable packer.

- **Severity:** Medium 6.6 (`CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 26 Mar 2021
- **Updated:** 3 Aug 2024
- **Also known as:** DEBIAN-CVE-2021-20285, GHSA-9235-qgm5-877x, UBUNTU-CVE-2021-20285

## What is CVE-2021-20285?

CVE-2021-20285 is a medium-severity memory corruption vulnerability in upx, published on 26 Mar 2021. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.

### Official description

A flaw was found in upx canPack in p_lx_elf.cpp in UPX 3.96. This flaw allows attackers to cause a denial of service (SEGV or buffer overflow and application crash) or possibly have unspecified other impacts via a crafted ELF. The highest threat from this vulnerability is to system availability.

Weakness: CWE-787 (Out-of-bounds Write), CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer)

## Which versions are affected by CVE-2021-20285?

It affects 1 product.


Products: Upx Upx.

## How do I fix CVE-2021-20285?

Upgrade to a fixed version.

## Is CVE-2021-20285 being exploited?

There is no known exploitation of CVE-2021-20285 in the wild and no public exploit code.

## Other vulnerabilities in upx

- [CVE-2020-27796](https://insights.sbomify.com/CVE-2020-27796/): Memory corruption in upx (high 7.8)
- [CVE-2020-27799](https://insights.sbomify.com/CVE-2020-27799/): Memory corruption in upx (high 7.8)
- [CVE-2020-27800](https://insights.sbomify.com/CVE-2020-27800/): Memory corruption in upx (high 7.8)
- [CVE-2020-27801](https://insights.sbomify.com/CVE-2020-27801/): Memory corruption in upx (high 7.8)
- [CVE-2019-14296](https://insights.sbomify.com/CVE-2019-14296/): Memory corruption in n/a (high 7.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-20285 and fix it if it is affected.

What it is: CVE-2021-20285 is a medium-severity memory corruption vulnerability in upx, published on 26 Mar 2021. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2021-20285 in the wild and no public exploit code.

Affected product: upx. 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-2021-20285/ (Markdown: https://insights.sbomify.com/CVE-2021-20285/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-20285
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-20285
- OSV: https://osv.dev/vulnerability/CVE-2021-20285

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-20285/
Summaries are generated and may contain mistakes; the official description above is the record.