# CVE-2026-102471: CRLF header injection in vertx-mail-client allows manipulation of outgoing SMTP messages

> Attackers can inject CRLF sequences into SMTP headers to manipulate outgoing email content and structure via the Vert.x mail client library.

- **Severity:** Medium 6.9 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 14 Oct 2026
- **Updated:** 14 Oct 2026
- **Also known as:** GHSA-762q-q3hx-6c35, GHSA-rm5c-2c7f-gc5g

## What is CVE-2026-102471?

CVE-2026-102471 is a medium-severity vulnerability in Eclipse Vert.x, published on 14 Oct 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

In Eclipse Vert.x versions [4.0.0, 4.5.34] or [5.0.0,5.0.12] or [5.1.0,5.1.9] or [5.2.0, 5.2.0], the vertx-mail-client does not sanitize CR (\r) or LF (\n) characters in user-supplied email header names and values before writing them into the SMTP DATA section. A CR/LF sequence embedded in a name or value passed to MailMessage.addHeader(), MailMessage.setHeaders(), MailAttachment.addHeader(), or MailAttachment.setHeaders() is written verbatim to the wire, allowing an attacker to inject arbitrary headers (e.g. Bcc, Reply-To, Content-Type) or prepend body content to the outgoing message.

The same weakness affects MIME part metadata set via MailAttachment.setContentType(), setDisposition(), setDescription(), and setContentId(), which are written directly into MIME part headers without validation.

A secondary weakness in Utils.mustEncode(char) additionally allows a bare LF in a From display-name to bypass Q-encoding and reach the wire unchanged.

An unauthenticated attacker who can control any header name, header value, or attachment metadata field passed to the mail client (for example via a web form or API that feeds into MailMessage) can exploit this to redirect email copies, spoof headers, or tamper with message structure.

The impacted component is io.vertx:vertx-mail-client.

Weakness: CWE-93 (Improper Neutralization of CRLF Sequences)

## Which versions are affected by CVE-2026-102471?

It affects 1 product.


Products: Eclipse Vert.x.

## How do I fix CVE-2026-102471?

No fix has been published for CVE-2026-102471 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-102471 being exploited?

There is no known exploitation of CVE-2026-102471 in the wild and no public exploit code.

## Other vulnerabilities in Eclipse Vert.x

- [CVE-2019-17640](https://insights.sbomify.com/CVE-2019-17640/): Path Traversal in Eclipse Vert (critical 9.8)
- [CVE-2018-12542](https://insights.sbomify.com/CVE-2018-12542/): Eclipse Vert.x does not properly neutralize '' (forward slashes) sequences that can resolve to an external location (critical 9.8)
- [CVE-2018-12544](https://insights.sbomify.com/CVE-2018-12544/): Moderate severity vulnerability that affects io.vertx:vertx-core (critical 9.8)
- [CVE-2026-102469](https://insights.sbomify.com/CVE-2026-102469/): Deserialization in Eclipse Vert.x (critical 9.2)
- [CVE-2018-12540](https://insights.sbomify.com/CVE-2018-12540/): High severity vulnerability that affects io.vertx:vertx-web (high 8.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-102471 and fix it if it is affected.

What it is: CVE-2026-102471 is a medium-severity vulnerability in Eclipse Vert.x, published on 14 Oct 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-2026-102471 in the wild and no public exploit code.

Affected product: Eclipse Vert.x. 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-2026-102471/ (Markdown: https://insights.sbomify.com/CVE-2026-102471/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-102471
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-102471
- OSV: https://osv.dev/vulnerability/CVE-2026-102471

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-102471/
Summaries are generated and may contain mistakes; the official description above is the record.