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Home / Threats / CVE-2026-23829

CVE-2026-23829 - Mailpit Plugin

CVE-2026-23829

Vulnerability CVE-2026-23829 PLUGIN mailpit MEDIUM

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.

CVE-2026-23829

MEDIUM CVSS 5.3 Published 2026-01-19 Updated 2026-02-23
AI Risk Elevated (56/100) Active Exploit: No strong signal Published Exploit: Public exploit references found Priority: P3 Priority
Severity Band MEDIUM
CVSS Vector CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
Affected Components 1
Reference Links 3
AI Risk Engine Elevated (56/100)
Exploitability Medium
Active Exploitation No strong signal
Published Exploit Status Public exploit references found

Threat Timeline

  1. 2026-01-19 CVE published and first recorded in the threat feed.
  2. 2026-02-23 Record updated with latest vulnerability metadata.
  3. 2026-04-09 AI technical context refreshed for mitigation and impact guidance.
  4. Now Monitoring for follow-up changes, linked references, and new related CVEs.

AI Context

Machine-generated threat intelligence

AI Updated 14 days ago

AI enriched 14 days ago (2026-04-09 06:30 UTC)

Technical Summary

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…

Potential Impact

Severity is MEDIUM (CVSS 5.3). Depending on deployment context, affected components may be exposed to unauthorized actions or data integrity risk.

Exploitability Assessment

Exploitability is assessed as Medium based on published exploit references.

Primary risk drivers: published exploit references

Mitigation Recommendations

Validate affected product versions, prioritize patching, and monitor references for vendor remediation guidance. If immediate patching is not possible, apply compensating controls and limit exposure of vulnerable surfaces.

Detection & Monitoring

Track authentication anomalies, unexpected file writes, and suspicious plugin API activity around affected components.

Business Impact Lens

Prioritize remediation where affected components process customer data, admin sessions, or Internet-exposed workflows.

Affected Products

Mailpit PLUGIN · mailpit Affected: >= 1.28.3, <= 1.28.3 Fixed version not specified
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