# CVE-2020-28020: Integer overflow in n/a

> An unauthenticated remote attacker can execute arbitrary code on Exim mail servers due to an integer overflow in header processing.

- **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:** 6 May 2021
- **Updated:** 4 Aug 2024
- **Also known as:** CLEANSTART-2025-KN85431, DEBIAN-CVE-2020-28020, GHSA-p795-3xjq-48vx, UBUNTU-CVE-2020-28020

## What is CVE-2020-28020?

CVE-2020-28020 is a critical vulnerability in Exim Exim, published on 6 May 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Exim 4 before 4.92 allows Integer Overflow to Buffer Overflow, in which an unauthenticated remote attacker can execute arbitrary code by leveraging the mishandling of continuation lines during header-length restriction.

Weakness: CWE-190 (Integer Overflow or Wraparound)

## Which versions are affected by CVE-2020-28020?

It affects 1 product.


Products: Exim Exim.

## How do I fix CVE-2020-28020?

Upgrade to a fixed version.

## Is CVE-2020-28020 being exploited?

There is no known exploitation of CVE-2020-28020 in the wild and no public exploit code.

## Other vulnerabilities in Exim Exim

- [CVE-2026-45185](https://insights.sbomify.com/CVE-2026-45185/): Use after free in Exim (critical 9.8)
- [CVE-2023-42115](https://insights.sbomify.com/CVE-2023-42115/): Exim AUTH Out-Of-Bounds Write Remote Code Execution Vulnerability (critical 9.8)
- [CVE-2020-28017](https://insights.sbomify.com/CVE-2020-28017/): Integer overflow in n/a (critical 9.8)
- [CVE-2020-28018](https://insights.sbomify.com/CVE-2020-28018/): Use after free in n/a (critical 9.8)
- [CVE-2020-28022](https://insights.sbomify.com/CVE-2020-28022/): Memory corruption in n/a (critical 9.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2020-28020 and fix it if it is affected.

What it is: CVE-2020-28020 is a critical vulnerability in Exim Exim, published on 6 May 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-2020-28020 in the wild and no public exploit code.

Affected product: Exim Exim. 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-2020-28020/ (Markdown: https://insights.sbomify.com/CVE-2020-28020/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2020-28020
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2020-28020
- OSV: https://osv.dev/vulnerability/CVE-2020-28020

---
From sbomify Insights: https://insights.sbomify.com/CVE-2020-28020/
Summaries are generated and may contain mistakes; the official description above is the record.