Vikunja has HTML Injection via Task Titles in Overdue Email Notifications

Exploitation

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

CVSS

5.4 · CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N

EPSS

• CVE-2026-35600: 0.19% estimated exploitation activity in the next 30 days; percentile 9.26 (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 Task titles are embedded directly into Markdown link syntax in overdue email notifications without escaping Markdown special characters. When rendered by goldmark and sanitized by bluemonday (which allows <a and <img tags), injected Markdown constructs produce phishing links and tracking pixels in legitimate notification emails. Details The overdue task notification at pkg/models/notifications.go:360 constructs a Markdown list entry: The task title is placed inside Markdown link syntax TITLE. A title containing ] and breaks the link structure. The assembled Markdown is converted to HTML by goldmark at pkg/notifications/mailrender.go:214, then sanitized by bluemonday's UGCPolicy. Since UGCPolicy intentionally allows <a href and <img src with http/https URLs, the injected links and images survive sanitization and reach the email recipient. The same pattern affects multiple notification types at notifications.go lines 72, 176, 227, and 318. Proof of Concept Tested on Vikunja…

Published by the source

10 Apr 2026, 15:34 UTC

Last modified by the source

10 Apr 2026, 19:45 UTC

Source last checked

26 Oct 2026, 15:19 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-45q4-x4r9-8fqj

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# Patch Next advisory brief: CVE-2026-35600

Advisory: Vikunja has HTML Injection via Task Titles in Overdue Email Notifications
IDs: CVE-2026-35600, GHSA-45q4-x4r9-8fqj
Record: https://patchnext.com/advisories/cve-2026-35600 (revision 1, source checked 26 Oct 2026, 15:19 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.4)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: code.vikunja.io/api 2.3.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go code.vikunja.io/api: affected <= 2.2.2; fixed in 2.3.0

## Suggested inspection (read-only)
- Go code.vikunja.io/api: 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 code.vikunja.io/api.
- 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://github.com/advisories/GHSA-45q4-x4r9-8fqj (GitHub-reviewed advisory GHSA-45q4-x4r9-8fqj lists affected ranges: Go code.vikunja.io/api >=0 <=2.2.2)

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