# CVE-2026-45185: Use after free in Exim

> An unauthenticated attacker can execute arbitrary code on Exim mail servers using GnuTLS by triggering a use-after-free during TLS chunking transfers.

- **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:** 12 May 2026
- **Updated:** 14 May 2026
- **Also known as:** CLSA-2026-1781269872, DEBIAN-CVE-2026-45185, GHSA-fhg4-whcv-f8v4, UBUNTU-CVE-2026-45185, USN-8270-1

## What is CVE-2026-45185?

CVE-2026-45185 is a critical use after free vulnerability in Exim Exim, published on 12 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Exim before 4.99.3, in certain GnuTLS configurations, has a remotely reachable use-after-free in the BDAT body parsing path. It is triggered when a client sends a TLS close_notify mid-body during a CHUNKING transfer, followed by a final cleartext byte on the same TCP connection. This can lead to heap corruption. An unauthenticated network attacker exploiting this vulnerability could execute arbitrary code.

Weakness: CWE-416 (Use After Free)

## Which versions are affected by CVE-2026-45185?

It affects 1 product.


Products: Exim Exim.

## How do I fix CVE-2026-45185?

Upgrade to a fixed version.

## Is CVE-2026-45185 being exploited?

There is no known exploitation of CVE-2026-45185 in the wild and no public exploit code.

Public exploit code:

- POC_CVE-2026-45185 for nuclei-templates (github_poc): https://github.com/MJ-bin/POC_CVE-2026-45185
- Dead.Letter CVE-2026-45185 EXIM Vulnerability Detection Script (github_poc): https://github.com/liamromanis101/Dead.Letter-CVE-2026-45185
- These detection scripts are property of the SECPlayground Platform.  Two safe detection scripts. Neither drives the close_notify-mid-BDAT trigger, so they will not crash the daemon or leave panic-log entries.  Both verdicts are "likely vulnerable" — distinguishing GnuTLS from OpenSSL builds remotely is not reliable without exploitation. (github_poc): https://github.com/materaj2/cve-2026-45185-detection-script
- https://github.com/0init/CVE-2026-45185 (github_poc): https://github.com/0init/CVE-2026-45185

## Other vulnerabilities in Exim Exim

- [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-2020-28020](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-2026-45185 and fix it if it is affected.

What it is: CVE-2026-45185 is a critical use after free vulnerability in Exim Exim, published on 12 May 2026. 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-2026-45185 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-2026-45185/ (Markdown: https://insights.sbomify.com/CVE-2026-45185/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-45185
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-45185
- OSV: https://osv.dev/vulnerability/CVE-2026-45185

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-45185/
Summaries are generated and may contain mistakes; the official description above is the record.