Header Injection Vulnerability in Mailpit Email Testing Tool by Axllent
CVE-2026-23829

5.3MEDIUM

Key Information:

Vendor: Axllent
Status: Mailpit
Vendor: CVE Published:; 18 January 2026

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👾 Exploit Exists🟡 Public PoC

What is CVE-2026-23829?

Mailpit, an email testing tool developed by Axllent, has a vulnerability in its SMTP server that allows attackers to exploit insufficient validation in the regular expression used for validating RCPT TO and MAIL FROM addresses. This flaw enables attackers to inject arbitrary SMTP headers, potentially compromising email integrity and allowing for further manipulation of email interactions. The vulnerability arises from the regex not adequately filtering control characters, specifically carriage return characters ( ) and line feed characters ( ). Users are advised to upgrade to version 1.28.3 or later to mitigate this risk.

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Affected Version(s)

mailpit < 1.28.3

Exploit Proof of Concept (PoC)

PoC code is written by security researchers to demonstrate the vulnerability can be exploited. PoC code is also a key component for weaponization which could lead to ransomware.

CTT-Mailpit-RCE-v1.0---Temporal-Resonance-Mail-Server-Takeover
Created by SimoesCTT

-CVE-2026-23829-CTT-Mailpit-phase-reconstruction-
Created by SimoesCTT