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Vulnerability record · CVE-2026-23829 · published 19 January 2026

CVE-2026-23829: Axllent mailpit vulnerability

Axllent · Mailpit

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.

5.3 CVSS 3.1 Medium EPSS 1.4% · top 28.2% CWE-93 · CWE-93CWE-150 · CWE-150
5.3CVSS 3.1 base score
1.4%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
3References, 1 tagged exploit
17 Jun 2026Last modified by NVD

Description

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.

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://github.com/axllent/mailpit/commit/36cc06c125954dec6673219dafa084e13cc14534 Patch
https://github.com/axllent/mailpit/releases/tag/v1.28.3 ProductRelease Notes
https://github.com/axllent/mailpit/security/advisories/GHSA-54wq-72mp-cq7c ExploitMitigationThird Party Advisory

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Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

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Source: NIST National Vulnerability Database (record CVE-2026-23829), CISA KEV, FIRST EPSS (scores of 2026-09-27). This page is refreshed as NVD updates the record.