# CVE-2026-67446: Mailpit thumbnail generation unbounded image dimension decode

Source: https://junglewise.ai/threats/cve-2026-67446-mailpit-thumbnail-generation-unbounded-image-dimension-decode  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-08-20. Updated: 2026-09-25  
License: CC BY 4.0 with a link back

CVE-2026-67446 · Severity: high · CVSS 7.5 · Published 2026-08-20

Mailpit's image thumbnail feature can be exploited by sending specially crafted email attachments that appear small when compressed but expand to hundreds of megabytes when decoded. An attacker can repeatedly request thumbnail generation through the API or by opening emails in the web UI, causing excessive memory and CPU consumption that leads to denial of service. The issue affects the default unauthenticated API configuration.

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

## Quick answers

**Is CVE-2026-67446 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-67446 being exploited in the wild.

**How severe is CVE-2026-67446?** High severity, with a CVSS score of 7.5, published 20 August 2026.

**Which products and versions are affected?** Axllent Mailpit <= 1.30.3; github.com/axllent/mailpit (Go) <= 1.30.3, SEMVER:introduced=0,fixed=1.30.4.

**Is there a fix for CVE-2026-67446?** Yes. github.com/axllent/mailpit (Go): upgrade to 1.30.4 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-67446 attacked?** It is attacked over the network, in a web application.

**Am I affected by CVE-2026-67446?** Check whether you run Axllent Mailpit or 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 1.30.4 or later

  ```sh
  go get github.com/axllent/mailpit@v1.30.4
  ```


## Technical details

The vulnerability is a resource-exhaustion flaw in the thumbnail handler (`server/apiv1/thumbnails.go`) that processes image attachments via the `GET /api/v1/message/{id}/part/{partID}/thumb` endpoint. The handler calls `imaging.Decode()` on untrusted attachment content before checking decoded pixel dimensions or memory budget, resulting in unbounded raster allocation. A malicious PNG can declare 4096×4096 dimensions (67 MB decoded) while remaining only 65 KB compressed; the endpoint then allocates and decodes the full image before scaling to the fixed 180×120 output size. The default message-size controls do not prevent this because they limit encoded message bytes, not decoded raster size. The endpoint is reachable by unauthenticated clients on default deployments, and opening image attachments in the web UI automatically triggers the vulnerable path. Patch version 1.30.4 adds dimension and pixel-budget checks before full image decode.

## Affected products

- axllent Mailpit <= 1.30.3

## Identifiers

- CVE-2026-67446
- GHSA-75mr-qw9x-3r39
- GO-2026-6359

## Timeline

- 2026-07-09: disclosed
- 2026-09-02: advisory: GHSA-75mr-qw9x-3r39 published
- 2026-09-02: patched: Fixed in version 1.30.4

## References

- [https://api.github.com/users/rexpository](https://api.github.com/users/rexpository)
- [https://github.com/rexpository](https://github.com/rexpository)
- [https://api.github.com/users/rexpository/gists%7B/gist_id%7D](https://api.github.com/users/rexpository/gists%7B/gist_id%7D)
- [https://api.github.com/users/rexpository/repos](https://api.github.com/users/rexpository/repos)
- [https://avatars.githubusercontent.com/u/30176934?v=4](https://avatars.githubusercontent.com/u/30176934?v=4)
- [https://api.github.com/users/rexpository/events%7B/privacy%7D](https://api.github.com/users/rexpository/events%7B/privacy%7D)

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- [Axllent Mailpit WebSocket origin check bypass via percent-encoded path](https://junglewise.ai/threats/cve-2026-67448-axllent-mailpit-websocket-origin-check-bypass-via-percent-encoded)
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- [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)