Vulnerability in Axllent Mailpit
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.
Vulnerability class: CRLF Injection
Published · last modified .
CVSS v3 metric
CVSS v3 base score 5.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N.
EPSS exploit prediction
EPSS: 0.014 (71.8th percentile), scored .
Low probability of exploitation in the next 30 days, but still tracked. 72nd percentile — 71.8% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.014 · newest: 0.014 · change: -0.000
Affected products
- Axllent Mailpit — versions < 1.28.3
Weakness classification (CWE)
Public proof-of-concept exploits
References
- github.com/axllent/mailpit/security/advisories/GHSA-54wq-72mp-cq7c (Exploit, Third Party Advisory, Mitigation)
- github.com/axllent/mailpit/commit/36cc06c125954dec6673219dafa084e13cc14534 (Patch)
- github.com/axllent/mailpit/releases/tag/v1.28.3 (Product, Release Notes)
Frequently asked questions
- What is CVE-2026-23829?
- CVE-2026-23829 is a medium-severity vulnerability in Axllent Mailpit, classified under CRLF Injection. CVSS score: 5.3/10. Published 2026-01-19.
- How severe is CVE-2026-23829?
- Medium severity. CVSS v3 base score is 5.3 out of 10.
- Is CVE-2026-23829 known to be exploited?
- 2 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.