CVE-2026-91971

Vikunja before 2.6.0 fails to apply pixel decode limits to avatar and project-background upload endpoints, allowing authenticated users to upload crafted images that decode to excessive pixel counts. Attackers can upload small images with extreme aspect ratios that consume significant CPU and memory during processing, causing denial of service through repeated or concurrent uploads.

Vikunja before 2.6.0 fails to apply pixel decode limits to avatar and project-background upload endpoints, allowing authenticated users to upload crafted images that decode to excessive pixel counts. Attackers can upload small images with extreme aspect ratios that consume significant CPU and memory during processing, causing denial of service through repeated or concurrent uploads.

Summary

The 50-megapixel decode guard exists only on the task-attachment preview path. Avatar and project-background uploads decode uploaded images with no pixel cap. Worse, the avatar resize fixes the output height at 1024 and derives the width from the aspect ratio, so a tiny extreme-aspect-ratio PNG expands to an enormous output image — an input-side pixel cap would not catch it.

Details

The only maxPixels check (50MP) is in TaskAttachment.GetPreview (pkg/models/task_attachment.go ~lines 332-338). No such check guards:

• avatar upload: pkg/modules/avatar/upload/upload.go (~lines 82, 137, 141)
• project background: pkg/modules/background/handler/background.go (~lines 174, 269, 289)

imaging.Resize(img, 0, 1024, imaging.Lanczos) (upload.go ~line 141) fixes height=1024 and derives width from the aspect ratio: a 20000x10 input yields a ~2,048,000 x 1024 output (~2.1 billion pixels), so a few-hundred-byte file drives huge CPU and memory.

PoC (verified at runtime against v2.5.0)

PUT /api/v1/user/settings/avatar/upload   avatar=8000x8000 PNG (64MP, 192KB) -> 200 (accepted; exceeds the 50MP attachment cap)
PUT /api/v1/user/settings/avatar/upload   avatar=20000x10 PNG (681 bytes)    -> 200 after ~19.6s of server processing

Contrast (guard present): uploading the 64MP PNG as a task attachment and requesting its preview returns in ~1ms without decoding — GetPreview rejects it via maxPixels and falls back to the raw file.

Impact

A small crafted upload drives disproportionate CPU and memory on the avatar and background paths. Repeated or concurrent requests can exhaust server resources. Amplification comes from both the missing input pixel cap and the height-fixed resize, so an input-side cap alone is insufficient.

Fix

Apply a pixel-dimension cap (as on the attachment path) to the avatar and background decode paths, and bound the resize output dimensions (cap width as well as height).

Duplicate Advisory

This advisory has been withdrawn because it is a duplicate of GHSA-4vh2-39rq-rq8j. This link is maintained to preserve external references.

Original Description

Vikunja before 2.6.0 fails to apply pixel decode limits to avatar and project-background upload endpoints, allowing authenticated users to upload crafted images that decode to excessive pixel counts. Attackers can upload small images with extreme aspect ratios that consume significant CPU and memory during processing, causing denial of service through repeated or concurrent uploads.

Vikunja before 2.6.0 fails to apply pixel decode limits to avatar and project-background upload endpoints, allowing authenticated users to upload crafted images that decode to excessive pixel counts. Attackers can upload small images with extreme aspect ratios that consume significant CPU and memory during processing, causing denial of service through repeated or concurrent uploads.

Vikunja before 2.6.0 fails to apply pixel decode limits to avatar and project-background upload endpoints, allowing authenticated users to upload crafted images that decode to excessive pixel counts. Attackers can upload small images with extreme aspect ratios that consume significant CPU and memory during processing, causing denial of service through repeated or concurrent uploads.

Summary

The 50-megapixel decode guard exists only on the task-attachment preview path. Avatar and project-background uploads decode uploaded images with no pixel cap. Worse, the avatar resize fixes the output height at 1024 and derives the width from the aspect ratio, so a tiny extreme-aspect-ratio PNG expands to an enormous output image — an input-side pixel cap would not catch it.

Details

The only maxPixels check (50MP) is in TaskAttachment.GetPreview (pkg/models/task_attachment.go ~lines 332-338). No such check guards:

• avatar upload: pkg/modules/avatar/upload/upload.go (~lines 82, 137, 141)
• project background: pkg/modules/background/handler/background.go (~lines 174, 269, 289)

imaging.Resize(img, 0, 1024, imaging.Lanczos) (upload.go ~line 141) fixes height=1024 and derives width from the aspect ratio: a 20000x10 input yields a ~2,048,000 x 1024 output (~2.1 billion pixels), so a few-hundred-byte file drives huge CPU and memory.

PoC (verified at runtime against v2.5.0)

PUT /api/v1/user/settings/avatar/upload   avatar=8000x8000 PNG (64MP, 192KB) -> 200 (accepted; exceeds the 50MP attachment cap)
PUT /api/v1/user/settings/avatar/upload   avatar=20000x10 PNG (681 bytes)    -> 200 after ~19.6s of server processing

Contrast (guard present): uploading the 64MP PNG as a task attachment and requesting its preview returns in ~1ms without decoding — GetPreview rejects it via maxPixels and falls back to the raw file.

Impact

A small crafted upload drives disproportionate CPU and memory on the avatar and background paths. Repeated or concurrent requests can exhaust server resources. Amplification comes from both the missing input pixel cap and the height-fixed resize, so an input-side cap alone is insufficient.

Fix

Apply a pixel-dimension cap (as on the attachment path) to the avatar and background decode paths, and bound the resize output dimensions (cap width as well as height).

Duplicate Advisory

This advisory has been withdrawn because it is a duplicate of GHSA-4vh2-39rq-rq8j. This link is maintained to preserve external references.

Original Description

Vikunja before 2.6.0 fails to apply pixel decode limits to avatar and project-background upload endpoints, allowing authenticated users to upload crafted images that decode to excessive pixel counts. Attackers can upload small images with extreme aspect ratios that consume significant CPU and memory during processing, causing denial of service through repeated or concurrent uploads.

Vikunja: Unbounded image decode on avatar and project-background uploads enables decode/resize amplification in code.vikunja.io/api.

NOTE: The source advisory for this report contains additional versions that could not be automatically mapped to standard Go module versions.

(If this is causing false-positive reports from vulnerability scanners, please suggest an edit to the report.)

The additional affected modules and versions are: code.vikunja.io/api before v2.6.0.