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CVE-2026-23829

Mailpit has SMTP Header Injection via Regex Bypass

Public exploit available. Not confirmed exploited in the wild yet. Fixed in 1.28.3.

CVSS 3.15.3MediumEPSS percentile72nd1.4% chance in 30 daysCISA KEVNot listedNo confirmed exploitation
Public exploit: 1 sourceFix1.28.3Upgrade to this build

Published Updated Sources: CVE.org, NVD, GitHub

NVD CVE.org

What to do

Find your product and version, then upgrade to the build on the right.

  • Axllent MailpitAffected: < 1.28.3Upgrade to: not statedStated by: CVE record
  • Go github.com/axllent/mailpitAffected: < 1.28.3Upgrade to: 1.28.3Stated by: GitHub advisory

Versions as the sources state them. Full version matrix after sign-in

Check it yourselfA free Nuclei check exists for this CVE. Run it against your hosts.Is your organisation exposed?Discuss checks for your systems with a specialist. Scope is agreed before testing.

What it is

From the CVE record

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.

In plain language

No plain-language summary for this CVE yet.

Exploitation

Where each signal puts this CVE on the scale from published to confirmed exploited.

EPSS72nd
Public exploit
CISA KEV

Not in the catalog. CISA has not confirmed exploitation.

Public exploits

1 source with a proof of concept or module.

Exploit links, PoCs and Metasploit modules after sign-in
EPSS

1.4% chance of exploitation activity in the next 30 days, which ranks it in the 72nd percentile of scored CVEs.

Exploit Prediction Scoring System, FIRST.org. A probability, not a confirmation.

Lifecycle

The patch came 11 days before any public exploit.

  1. Nuclei check added
  2. Public exploit / PoCsource: github-poc
  3. Patch availableworkaround available, record updated
  4. Publishedweakness classified

Affected products

Technical detail

CVSS 3.1 vector

Open in the CVSS calculator

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

Scored 5.3 by NVD.

How it is reached

  • Attack Vector NetworkExploitable remotely over the network without any special conditions
  • Attack Complexity LowNo special conditions — the attack can be reliably reproduced
  • Privileges Required NoneNo authentication required — anyone can exploit this
  • User Interaction NoneNo user interaction needed — fully automated exploitation

Scope

  • Scope UnchangedImpact is limited to the vulnerable component itself

Impact if exploited

  • Confidentiality NoneNo confidentiality impact
  • Integrity LowData modification is possible but limited in scope or consequence
  • Availability NoneNo availability impact

Weaknesses

Sources

References in the record

And 2 more references. See all after sign-in

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