# CVE-2021-43313: Memory corruption in upx

> A heap-based buffer overflow in UPX allows attackers to execute arbitrary code or cause denial of service via crafted ELF files.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/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:** 24 Mar 2023
- **Updated:** 25 Feb 2025
- **Also known as:** DEBIAN-CVE-2021-43313, GHSA-j554-cfvx-c858, UBUNTU-CVE-2021-43313

## What is CVE-2021-43313?

CVE-2021-43313 is a high-severity memory corruption vulnerability in upx, published on 24 Mar 2023. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

A heap-based buffer overflow was discovered in upx, during the variable 'bucket' points to an inaccessible address. The issue is being triggered in the function PackLinuxElf32::invert_pt_dynamic at p_lx_elf.cpp:1688.

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-2021-43313?

It affects 1 product.


Products: Upx Upx.

## How do I fix CVE-2021-43313?

Upgrade to a fixed version.

## Is CVE-2021-43313 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2021-43313 exists.

## 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-2021-43313 and fix it if it is affected.

What it is: CVE-2021-43313 is a high-severity memory corruption vulnerability in upx, published on 24 Mar 2023. 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-2021-43313 exists.

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-2021-43313/ (Markdown: https://insights.sbomify.com/CVE-2021-43313/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-43313
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-43313
- OSV: https://osv.dev/vulnerability/CVE-2021-43313

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-43313/
Summaries are generated and may contain mistakes; the official description above is the record.