Mailpit: Thumbnail generation decodes unbounded image dimensions before scaling

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

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

EPSS

• CVE-2026-67446: 0.51% estimated exploitation activity in the next 30 days; percentile 43.30 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary Mailpit's thumbnail endpoint decodes attacker-supplied image attachments into a full raster before checking any decoded-pixel, dimension, or memory budget. A remote client that can store an email and reach the default web API can supply a compact high-dimension image, then request /api/v1/message/{id}/part/{partID}/thumb to force server-side memory and CPU work far larger than the encoded attachment size before Mailpit returns a 180x120 thumbnail. Technical Details The route is registered as GET /api/v1/message/{id}/part/{partID}/thumb in server/server.go. The handler in server/apiv1/thumbnails.go loads the requested attachment and accepts any part whose content type begins with image/: storage.GetAttachmentPart() reparses the stored raw email and returns the matching attacker-supplied attachment bytes. Thumbnail() then calls imaging.Decode() before any check on declared dimensions or estimated decoded bytes. The subsequent imaging.Fill(img, 180, 120, ...), imaging.Clone(),…

Published by the source

2 Sep 2026, 23:39 UTC

Last modified by the source

10 Sep 2026, 15:15 UTC

Source last checked

26 Oct 2026, 15:28 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-75mr-qw9x-3r39

2. Revision 2 · amended · 24 Oct 2026

   Amended from osv record GO-2026-6359

3. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-75mr-qw9x-3r39

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# Patch Next advisory brief: CVE-2026-67446

Advisory: Mailpit: Thumbnail generation decodes unbounded image dimensions before scaling
IDs: CVE-2026-67446, GHSA-75mr-qw9x-3r39
Record: https://patchnext.com/advisories/cve-2026-67446 (revision 3, source checked 26 Oct 2026, 15:28 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: github.com/axllent/mailpit 1.30.4. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/axllent/mailpit: affected <= 1.30.3; fixed in 1.30.4

## Suggested inspection (read-only)
- Go github.com/axllent/mailpit: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on github.com/axllent/mailpit.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-75mr-qw9x-3r39 (OSV record GHSA-75mr-qw9x-3r39 lists affected ranges: Go github.com/axllent/mailpit >=0 <1.30.4 (fixed))
- Verified: https://osv.dev/vulnerability/GO-2026-6359 (OSV record GO-2026-6359 lists affected ranges: Go github.com/axllent/mailpit >=0 <1.30.4 (fixed))
- Verified: https://github.com/advisories/GHSA-75mr-qw9x-3r39 (GitHub-reviewed advisory GHSA-75mr-qw9x-3r39 lists affected ranges: Go github.com/axllent/mailpit >=0 <=1.30.3)

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