# CVE-2023-42118: Exim libspf2 Integer Underflow Remote Code Execution Vulnerability

> Network-adjacent attackers can execute arbitrary code on Exim mail servers via an integer underflow in libspf2 SPF macro parsing.

- **Severity:** High 7.5 (`CVSS:3.0/AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 3 May 2024
- **Updated:** 28 Mar 2025
- **Also known as:** ALPINE-CVE-2023-42118, DEBIAN-CVE-2023-42118, GHSA-2vq7-8vvf-w66v, OESA-2024-2584, OESA-2024-2585, OESA-2024-2586, OESA-2025-1077, UBUNTU-CVE-2023-42118

## What is CVE-2023-42118?

CVE-2023-42118 is a high-severity vulnerability in Exim libspf2, published on 3 May 2024. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

Exim libspf2 Integer Underflow Remote Code Execution Vulnerability. This vulnerability allows network-adjacent attackers to execute arbitrary code on affected installations of Exim libspf2. Authentication is not required to exploit this vulnerability. 

The specific flaw exists within the parsing of SPF macros. When parsing SPF macros, the process does not properly validate user-supplied data, which can result in an integer underflow before writing to memory. An attacker can leverage this vulnerability to execute code in the context of the service account.
. Was ZDI-CAN-17578.

Weakness: CWE-191 (Integer Underflow (Wrap or Wraparound))

## Which versions are affected by CVE-2023-42118?

It affects 1 product.


Products: Libspf2 Project Libspf2.

## How do I fix CVE-2023-42118?

Apply the vendor's patch.

## Is CVE-2023-42118 being exploited?

There is no known exploitation of CVE-2023-42118 in the wild and no public exploit code.

## Other vulnerabilities in Exim libspf2

- [CVE-2021-33913](https://insights.sbomify.com/CVE-2021-33913/): Memory corruption in n/a (critical 9.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2023-42118 and fix it if it is affected.

What it is: CVE-2023-42118 is a high-severity vulnerability in Exim libspf2, published on 3 May 2024. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2023-42118 in the wild and no public exploit code.

Affected product: Exim libspf2. 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-2023-42118/ (Markdown: https://insights.sbomify.com/CVE-2023-42118/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2023-42118
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2023-42118
- OSV: https://osv.dev/vulnerability/CVE-2023-42118

---
From sbomify Insights: https://insights.sbomify.com/CVE-2023-42118/
Summaries are generated and may contain mistakes; the official description above is the record.