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

Medium 6.9 Published 14 Oct 2026 Updated 14 Oct 2026

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

Exploited in the wild: Not known
Login needed: Not needed
Attackable: Over the internet
Victim action needed: Not needed
Fix: None listed

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

Which versions are affected by CVE-2026-102471?

It affects 1 product.

Products include 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.

Sources

Also known as GHSA-762q-q3hx-6c35, GHSA-rm5c-2c7f-gc5g.