# CVE-2026-23829: GO-2026-4333 - Mailpit has an SMTP Header Injection via Regex Bypass in github.com/axllent/mailpit

Source: https://junglewise.ai/threats/cve-2026-23829-mailpit-has-an-smtp-header-injection-via-regex-bypass  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-02-03  
License: CC BY 4.0 with a link back

CVE-2026-23829 · Severity: low · CVSS 3.1 · Published 2026-02-03

Mailpit has an SMTP Header Injection via Regex Bypass in github.com/axllent/mailpit

Technologies: [github.com/axllent/mailpit (Go)](https://junglewise.ai/threats/technologies/github-com-axllent-mailpit). Vendors: [Go](https://junglewise.ai/threats/vendors/go).

## Quick answers

**Is CVE-2026-23829 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-23829 being exploited in the wild.

**How severe is CVE-2026-23829?** Low severity, with a CVSS score of 3.1, published 3 February 2026.

**Which products and versions are affected?** github.com/axllent/mailpit (Go) SEMVER:introduced=0,fixed=1.28.3.

**Is there a fix for CVE-2026-23829?** Yes. github.com/axllent/mailpit (Go): upgrade to 1.28.3 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**Am I affected by CVE-2026-23829?** Check whether you run github.com/axllent/mailpit (Go) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- github.com/axllent/mailpit (Go): upgrade to 1.28.3 or later

  ```sh
  go get github.com/axllent/mailpit@v1.28.3
  ```


## Affected products

- github.com/axllent/mailpit (Go) SEMVER:introduced=0,fixed=1.28.3

## Identifiers

- CVE-2026-23829
- GHSA-54wq-72mp-cq7c
- GO-2026-4333

## Related threats

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- [Mailpit SMTP DATA reader unbounded line buffering denial of service](https://junglewise.ai/threats/cve-2026-67447-mailpit-smtp-data-reader-unbounded-line-buffering-denial-of)
- [Mailpit thumbnail generation unbounded image dimension decode](https://junglewise.ai/threats/cve-2026-67446-mailpit-thumbnail-generation-unbounded-image-dimension-decode)
- [Mailpit SMTP command parser unbounded buffering denial of service](https://junglewise.ai/threats/cve-2026-67445-mailpit-smtp-command-parser-unbounded-buffering-denial-of-service)
- [axllent Mailpit memory exhaustion DoS in multiple API endpoints](https://junglewise.ai/threats/cve-2026-48824-axllent-mailpit-memory-exhaustion-dos-in-multiple-api-endpoints)