Vikunja has Algorithmic Complexity DoS in Repeating Task Handler

Exploitation

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

CVSS

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

EPSS

• CVE-2026-35599: 0.35% estimated exploitation activity in the next 30 days; percentile 28.40 (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 The addRepeatIntervalToTime function uses an O(n) loop that advances a date by the task's RepeatAfter duration until it exceeds the current time. By creating a repeating task with a 1-second interval and a due date far in the past, an attacker triggers billions of loop iterations, consuming CPU and holding a database connection for minutes per request. Details The vulnerable function at pkg/models/tasks.go:1456-1464: The RepeatAfter field accepts any positive integer (validated as range(0|9223372036854775807)), and DueDate accepts any valid timestamp including dates far in the past. When a task with repeatafter=1 and duedate=1900-01-01 is marked as done, the loop runs approximately 4 billion iterations (~60+ seconds of CPU time). Each request holds a goroutine and a database connection for the duration. With the default connection pool size of 100, approximately 100 concurrent requests exhaust all available connections. Proof of Concept Tested on Vikunja v2.2.2. Output: The…

Published by the source

10 Apr 2026, 15:34 UTC

Last modified by the source

10 Apr 2026, 19:36 UTC

Source last checked

26 Oct 2026, 15:19 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-r4fg-73rc-hhh7

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# Patch Next advisory brief: CVE-2026-35599

Advisory: Vikunja has Algorithmic Complexity DoS in Repeating Task Handler
IDs: CVE-2026-35599, GHSA-r4fg-73rc-hhh7
Record: https://patchnext.com/advisories/cve-2026-35599 (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 6.5)
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-r4fg-73rc-hhh7 (GitHub-reviewed advisory GHSA-r4fg-73rc-hhh7 lists affected ranges: Go code.vikunja.io/api >=0 <=2.2.2)

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