axllent mailpit up to 1.28.2 Regular Expression RCPT TO/MAIL FROM crlf injection

Summaryinfo

A vulnerability was found in axllent mailpit up to 1.28.2. It has been classified as problematic. Affected by this vulnerability is an unknown functionality of the component Regular Expression Handler. The manipulation of the argument RCPT TO/MAIL FROM leads to crlf injection. This vulnerability is traded as CVE-2026-23829. It is possible to initiate the attack remotely. There is no exploit available. Upgrading the affected component is recommended.

Detailsinfo

A vulnerability, which was classified as problematic, has been found in axllent mailpit up to 1.28.2. This issue affects an unknown code block of the component Regular Expression Handler. The manipulation of the argument RCPT TO/MAIL FROM with an unknown input leads to a crlf injection vulnerability. Using CWE to declare the problem leads to CWE-93. The product uses CRLF (carriage return line feeds) as a special element, e.g. to separate lines or records, but it does not neutralize or incorrectly neutralizes CRLF sequences from inputs. Impacted is integrity. The summary by CVE is:

Mailpit is an email testing tool and API for developers. Prior to version 1.28.3, Mailpit's SMTP server is vulnerable to Header Injection due to an insufficient Regular Expression used to validate `RCPT TO` and `MAIL FROM` addresses. An attacker can inject arbitrary SMTP headers (or corrupt existing ones) by including carriage return characters (`\r`) in the email address. This header injection occurs because the regex intended to filter control characters fails to exclude `\r` and `\n` when used inside a character class. Version 1.28.3 fixes this issue.

It is possible to read the advisory at github.com. The identification of this vulnerability is CVE-2026-23829 since 01/16/2026. The exploitation is known to be easy. The attack may be initiated remotely. No form of authentication is needed for a successful exploitation. Technical details of the vulnerability are known, but there is no available exploit.

Upgrading to version 1.28.3 eliminates this vulnerability. The upgrade is hosted for download at github.com. Applying the patch 36cc06c125954dec6673219dafa084e13cc14534 is able to eliminate this problem. The bugfix is ready for download at github.com. The best possible mitigation is suggested to be upgrading to the latest version.

The vulnerability is also documented in the databases at CNNVD (CNNVD-202601-2973), EUVD (EUVD-2026-3297) and CERT Bund (WID-SEC-2026-0146). Be aware that VulDB is the high quality source for vulnerability data.

Affected

• Open Source MailPit

Productinfo

Vendor

• axllent

Name

• mailpit

Version

• 1.28.0
• 1.28.1
• 1.28.2

License

• open-source

Website

• Product: https://github.com/axllent/mailpit/

CPE 2.3info

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CPE 2.2info

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Entryinfo

Be aware that VulDB is the high quality source for vulnerability data.

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