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CVE-2026-23829— Mailpit has SMTP Header Injection via Regex Bypass

Quick assessment

Affected
axllent mailpit
Exploitation
Public or AI PoC available; prioritize validation
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Mailpit是Ralph Slooten个人开发者的一个电子邮件测试工具。 Mailpit 1.28.3之前版本存在安全漏洞，该漏洞源于验证RCPT TO和MAIL FROM地址的正则表达式不足，可能导致标头注入。

CVSS 5.3 · Medium EPSS 1.42% · P72
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I. Basic Information for CVE-2026-23829

Vulnerability Information
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Vulnerability Title
Mailpit has SMTP Header Injection via Regex Bypass
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
对CRLF序列的转义处理不恰当(CRLF注入)
Source: CVE Program / CVE List V5
Vulnerability Title
Mailpit 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Mailpit是Ralph Slooten个人开发者的一个电子邮件测试工具。 Mailpit 1.28.3之前版本存在安全漏洞，该漏洞源于验证RCPT TO和MAIL FROM地址的正则表达式不足，可能导致标头注入。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
axllent mailpit < 1.28.3 -

II. Public POCs for CVE-2026-23829

# POC Description Source Link Shenlong Link
1 FROM HEADER INJECTION TO FULL RCE DOMINANCE The Original Flaw (CVE-2026-23829) · CVSS: 6.1/10 (Medium) - Header injection via regex bypass · Impact: Email spoofing, limited header manipulation · Reality: Boring, basic, barely worth weaponizing CTT Enhancement Revelation https://github.com/SimoesCTT/CTT-Mailpit-RCE-v1.0---Temporal-Resonance-Mail-Server-Takeover POC Details
2 It's a CRLF injection in Mailpit's SMTP server — a classic data corruption vulnerability. But under CTT, it's not just a bug. It's a phase reconstruction opportunity. https://github.com/SimoesCTT/-CVE-2026-23829-CTT-Mailpit-phase-reconstruction- POC Details
3 Mailpit < 1.28 contains a header injection caused by insufficient regex validation of `RCPT TO` and `MAIL FROM` addresses in the SMTP server, letting attackers inject arbitrary SMTP headers, exploit requires crafted email addresses https://github.com/projectdiscovery/nuclei-templates/blob/main/http/cves/2026/CVE-2026-23829.yaml POC Details
4 Mailpit < 1.28 contains a header injection caused by insufficient regex validation of `RCPT TO` and `MAIL FROM` addresses in the SMTP server, letting attackers inject arbitrary SMTP headers, exploit requires crafted email addresses https://github.com/projectdiscovery/nuclei-templates/blob/main/network/cves/2026/CVE-2026-23829.yaml POC Details
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III. Intelligence Information for CVE-2026-23829

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IV. Related Vulnerabilities

Same product: mailpit
Same vendor: axllent
Same weakness: CWE-93

V. Comments for CVE-2026-23829

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