CVE-2026-23829

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.

• CWE-93
• CWE-150

• https://github.com/axllent/mailpit/commit/36cc06c125954dec6673219dafa084e13cc14534Patch
• https://github.com/axllent/mailpit/releases/tag/v1.28.3Product, Release Notes
• https://github.com/axllent/mailpit/security/advisories/GHSA-54wq-72mp-cq7cExploit, Mitigation, Third Party Advisory

Published

Jan 19, 2026

Last Modified

Jun 17, 2026

Status

Analyzed

• How Strix found a critical auth bypass in etcdStrix autonomously discovered a critical authentication bypass in etcd, later designated CVE-2026-33413.
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