# CVE-2023-42115: Exim AUTH Out-Of-Bounds Write Remote Code Execution Vulnerability

> Remote attackers can execute arbitrary code on Exim mail servers via an out-of-bounds write in the SMTP service without authentication.

- **Severity:** Critical 9.8 (`CVSS:3.0/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:** 3 May 2024
- **Updated:** 20 Sep 2024
- **Also known as:** CLEANSTART-2025-UQ49615, DEBIAN-CVE-2023-42115, GHSA-67rj-8f2h-26fc, UBUNTU-CVE-2023-42115

## What is CVE-2023-42115?

CVE-2023-42115 is a critical memory corruption vulnerability in Exim Exim, published on 3 May 2024. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Exim AUTH Out-Of-Bounds Write Remote Code Execution Vulnerability. This vulnerability allows remote attackers to execute arbitrary code on affected installations of Exim. Authentication is not required to exploit this vulnerability. 

The specific flaw exists within the smtp service, which listens on TCP port 25 by default. The issue results from the lack of proper validation of user-supplied data, which can result in a write past the end of a buffer. An attacker can leverage this vulnerability to execute code in the context of the service account.
. Was ZDI-CAN-17434.

Weakness: CWE-787 (Out-of-bounds Write)

## Which versions are affected by CVE-2023-42115?

It affects 1 product.


Products: Exim Exim.

## How do I fix CVE-2023-42115?

Apply the vendor's patch.

## Is CVE-2023-42115 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2023-42115 exists.

Public exploit code:

- This module exploits a vulnerability in the target service identified as CVE-2023-42115. (github_poc): https://github.com/kirinse/cve-2023-42115
- https://github.com/doaso/CVE-2023-42115 (github_poc): https://github.com/doaso/CVE-2023-42115

## Other vulnerabilities in Exim Exim

- [CVE-2026-45185](https://insights.sbomify.com/CVE-2026-45185/): Use after free in Exim (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-2020-28020](https://insights.sbomify.com/CVE-2020-28020/): Integer overflow 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-2023-42115 and fix it if it is affected.

What it is: CVE-2023-42115 is a critical memory corruption vulnerability in Exim Exim, published on 3 May 2024. 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-2023-42115 exists.

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-2023-42115/ (Markdown: https://insights.sbomify.com/CVE-2023-42115/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2023-42115
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2023-42115
- OSV: https://osv.dev/vulnerability/CVE-2023-42115

---
From sbomify Insights: https://insights.sbomify.com/CVE-2023-42115/
Summaries are generated and may contain mistakes; the official description above is the record.