# CVE-2020-27798: Null dereference in upx

> A crafted Mach-O file causes a null pointer dereference in UPX, leading to a denial of service when processed.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/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:** 25 Aug 2022
- **Updated:** 4 Aug 2024
- **Also known as:** DEBIAN-CVE-2020-27798, GHSA-gqpc-4qr8-j9g3, UBUNTU-CVE-2020-27798

## What is CVE-2020-27798?

CVE-2020-27798 is a medium-severity vulnerability in upx, published on 25 Aug 2022. 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

An invalid memory address reference was discovered in the adjABS function in p_lx_elf.cpp in UPX 4.0.0 via a crafted Mach-O file.

Weakness: CWE-763 (Release of Invalid Pointer or Reference), CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer)

## Which versions are affected by CVE-2020-27798?

It affects 1 product.


Products: Upx Upx.

## How do I fix CVE-2020-27798?

Upgrade to a fixed version.

## Is CVE-2020-27798 being exploited?

There is no known exploitation of CVE-2020-27798 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-2020-27798 and fix it if it is affected.

What it is: CVE-2020-27798 is a medium-severity vulnerability in upx, published on 25 Aug 2022. 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-2020-27798 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-2020-27798/ (Markdown: https://insights.sbomify.com/CVE-2020-27798/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2020-27798
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2020-27798
- OSV: https://osv.dev/vulnerability/CVE-2020-27798

---
From sbomify Insights: https://insights.sbomify.com/CVE-2020-27798/
Summaries are generated and may contain mistakes; the official description above is the record.