CVE-2026-67446 Mailpit: Thumbnail generation decodes unbounded image dimensions before scaling
An attacker can cause denial of service by uploading crafted image attachments that consume excessive memory and CPU during thumbnail generation.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-67446?
CVE-2026-67446 is a medium-severity denial of service vulnerability in axllent mailpit, published on 20 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Mailpit is an email testing tool and API for developers. Prior to 1.30.4, Mailpit decodes attacker-supplied image attachments into a full raster before checking decoded dimensions, pixel count, or memory use in the GET /api/v1/message/{id}/part/{partID}/thumb endpoint. The Thumbnail handler in server/apiv1/thumbnails.go obtains attachment bytes through storage.GetAttachmentPart(), accepts image/* content, and calls imaging.Decode() with AutoOrientation before imaging.Fill() scales the image to 180 by 120 pixels. A compact image declaring very large dimensions can therefore consume disproportionately large memory and CPU, and opening the message UI can trigger the same endpoint through server/ui-src/components/message/MessageAttachments.vue. This can degrade availability when an unauthenticated client can store the crafted attachment and reach the web API. This issue is fixed in version 1.30.4.
Which versions are affected by CVE-2026-67446?
3 open source packages ship an affected version, including github.com/axllent/mailpit.
| Package | Affected | Fixed in |
|---|---|---|
github.com/axllent/mailpit Go | All versions | 1.30.4 |
github.com/axllent/mailpit Go | All versions | 1.30.4 |
github.com/axllent/mailpit Go | All versions | 1.30.4 |
How do I fix CVE-2026-67446?
Upgrade github.com/axllent/mailpit to 1.30.4 or later.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-67446 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-67446 exists.
Sources
Also known as GHSA-75mr-qw9x-3r39, GO-2026-6359.