How severe is CVE-2026-91971?

No CVSS score has been assigned to CVE-2026-91971 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2026-91971?

CVE-2026-91971 affects the following packages: code.vikunja.io/api (Go). Ecosystems affected: Go.

How do I fix CVE-2026-91971?

Update code.vikunja.io/api to 2.6.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-91971 is resolved across your whole dependency graph.

How do I detect CVE-2026-91971 in my Go dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for code.vikunja.io/api, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-91971 if there is no patch (or I can't update yet)?

Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

Is CVE-2026-91971 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-91971 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-91971?

CVE-2026-91971 has an EPSS (Exploit Prediction Scoring System) score of 0.4%, placing it in the 38th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-91971?

CVE-2026-91971 is classified as Uncontrolled Resource Consumption (CWE-400). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-91971 published, and has it been updated?

CVE-2026-91971 was published on September 15, 2026 and was last updated on October 28, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐹 Go

Not in CISA KEV

CVE-2026-91971 — api

Fix: go-vikunja/vikunja#3688

CVE-2026-91971 is a Uncontrolled Resource Consumption vulnerability in code.vikunja.io/api. A fix is available for code.vikunja.io/api — see the affected versions and patch details below.

Vikunja before 2.6.0 Denial of Service via Avatar Upload

Also known asGHSA-4vh2-39rq-rq8jGO-2026-6717

Published

Sep 15, 2026

Updated

Oct 28, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Oct 30, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

Proof-of-concept exploit code exists

CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-91971.

EPSS Exploitation Probability

via FIRST.org ↗

0.4%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs38th percentile — riskier than 38% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

1 pkg affected

🐹code.vikunja.io/api

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.

Description

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).

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐹Go	`code.vikunja.io/api`	all versions	2.6.0`go get code.vikunja.io/api@v2.6.0`

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for code.vikunja.io/api, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update code.vikunja.io/api to 2.6.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-91971 is resolved across your whole dependency graph.
Workarounds
Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

Frequently Asked Questions

### 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` (~

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