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Vulnerability · Published Aug 20, 2026 · Assigned by GitHub_M

CVE-2026-67446Mailpit: Thumbnail generation decodes unbounded image dimensions before scaling

Medium 5.3

In plain English

A medium-severity uncontrolled resource consumption in mailpit from axllent. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.5% (higher than 43% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)5.3Medium
Exploit odds (30 days)0.5%top 56.6% of all CVEs
Exploited in the wildNo reportsCISA SSVC: poc
Attack toolingNoneno public tooling known

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.

Affected packages & fixed versions

EcosystemPackageFixed inAdvisory
Gogithub.com/axllent/mailpit1.30.4GHSA-75mr-qw9x-3r39
Gogithub.com/axllent/mailpit1.30.4GO-2026-6359

Affected products (as reported)

VendorProductVersions
axllent mailpit < 1.30.4

Weakness: CWE-400, CWE-770 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

References