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Vikunja EUVDEUVD-2026-78654

| CVE-2026-91983 MEDIUM
Incorrect Authorization (CWE-863)
5.3
CVSS 4.0 · Vendor: VulnCheck
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Vulnerability Assessment

Weakness
CWE
OWASP Top 10:2025
A01:2025 - Broken Access Control
ASVS 5.0
V8 - Authorization Authorization logic validation
MITRE ATT&CK

1 technique across 1 tactic: Privilege Escalation

The technique list with ATT&CK links and the kill-chain view is part of the Basic plan and up.

This Month Plan within 30 days. Why: MEDIUM severity (CVSS 4.0-6.9).
Patch available 0.3% exploitation probability (EPSS)

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AnalysisAIv1 – Sep 15, 2026

An API token scope bypass in Vikunja before 2.6.0 allows a holder of a deliberately limited-scope API token to read task data outside that token's permissions — specifically comments, reactions, and time entries — by adding the 'expand' query string parameter to task read requests, because the authorization layer never inspects query parameters. Exploitation requires an already-valid low-privilege token (CVSS 4.0 PR:L) and only results in limited confidentiality loss, giving a modest base score of 5.3; there is no public exploit and no evidence of active exploitation at time of analysis. The vendor has released a fix in Vikunja 2.6.0.

Affected VersionsENISA

vikunja 1.0.0 <2.6.0

Affected Packages

go code.vikunja.io/api fix: 2.6.0
euvd vikunja fix: 2.6.0

Source: OSV (Open Source Vulnerabilities)

Affects your stack

Affects 2 packages in go, euvd

Checking this CVE against your own stacks and servers is part of the Basic plan and up.

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  • Exploit and PoC references, threat intelligence from 22 sources

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Severity by source

Vendor (VulnCheck) PRIMARY 5.3 MEDIUM
CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N

Primary rating from Vendor (VulnCheck) · only source for this CVE.

CVSS VectorVendor: VulnCheck

Attack Vector
Network
Attack Complexity
Low
Attack Requirements
None
Privileges Required
Low
User Interaction
None
Vulnerable system: Confidentiality
Low
Vulnerable system: Integrity
None
Vulnerable system: Availability
None
Subsequent system: Confidentiality
None
Subsequent system: Integrity
None
Subsequent system: Availability
None

Lifecycle Timeline

1
Patch available
Sep 15, 2026 - 16:03 EUVD

DescriptionCVE.org

Vikunja before 2.6.0 contains an API token scope bypass vulnerability in task read endpoints where authorization fails to inspect query string parameters. Attackers with limited token scopes can use the expand parameter to access restricted data like comments, reactions, and time entries without proper permission verification.

Threat Intelligence Overview

EPSS Score
0.3%
Top 81% exploitable
Threat Intel
1
1 sources
Exploit
POC
Public exploit code exists
Data Quality
6 sources
Confidence: High
EUVD NVD CVE.org EPSS Vulnrichment GHSA GitHub

How this decision was reached

The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.

SignalValue
Severity MEDIUM
CISA KEV No
Public POC Yes
EPSS 0.3%
Patch available Yes
Active threat No
Deciding rule
MEDIUM severity (CVSS 4.0-6.9)
What every action level means
Emergency Immediate action required. Criteria: CRITICAL + in CISA KEV (actively exploited) without patch, OR CRITICAL + EPSS > 30% without patch, OR CRITICAL + active threat signals without patch.
Act Now Prioritize within 24-48h. Criteria: in KEV with patch available, OR CRITICAL + public POC, OR HIGH + EPSS > 10%, OR CRITICAL + active threat, OR any CRITICAL severity.
This Week Schedule remediation this week. Criteria: HIGH severity (CVSS 7.0-8.9). Patch within normal change window.
This Month Plan within 30 days. Criteria: MEDIUM severity (CVSS 4.0-6.9), lower exploitation probability. Include in regular patch cycle.
Monitor Track and reassess. Criteria: LOW severity (CVSS 0.1-3.9), minimal exploitation risk. No immediate action needed.

SSVC AssessmentENISA

SSVC Decision· derived
Scheduled
Exploitation
Poc
System Exposure· derived
Open
Automatable
No
Human Impact· derived
Medium
Technical Impact
Partial

Priority Score

46
Low Medium High Critical
KEV: 0
EPSS: 0
CVSS: +26
PoC: +20
Weaponized: 0
Threat intel: 0
Gov advisory: 0

Attack Technique

Authentication bypass attacks exploit flaws in the verification mechanisms that control access to systems and applications.

CVE-2026-68582 CRITICAL POC
9.3 Aug 02

Cross-tenant information disclosure in the self-hosted task manager Vikunja (0.24.0 through 2.3.0) lets a holder of any

CVE-2026-27575 CRITICAL POC
9.1 Feb 25

Weak password policy in Vikunja task management before 2.0.0 allows users to set trivially guessable passwords. PoC avai

CVE-2026-68581 HIGH POC
8.6 Aug 02

Principal type confusion in Vikunja (versions 0.22.0-2.3.0) allows an authenticated low-privilege attacker to fully cont

CVE-2026-27616 HIGH POC
7.3 Feb 25

Stored cross-site scripting (XSS) in Vikunja prior to version 2.0.0 allows authenticated attackers to steal authenticati

CVE-2026-27819 HIGH POC
7.2 Feb 25

Vikunja before version 2.0.0 contains a path traversal vulnerability in its backup restoration function that fails to va

CVE-2026-27116 MEDIUM POC
6.1 Feb 25

Vikunja is an open-source self-hosted task management platform. [CVSS 6.1 MEDIUM]

CVE-2026-28268 CRITICAL
9.8 Feb 27

Business logic vulnerability in Vikunja task management platform before 2.1.0 allows incomplete resource cleanup, potent

CVE-2026-56765 CRITICAL
9.3 Jul 10

Instance-wide data breach in Vikunja before 2.2.1 lets remote attackers exfiltrate and destroy every file attachment acr

CVE-2026-34727 CRITICAL
9.1 Apr 10

Vikunja's OIDC callback handler issues a full JWT to any successfully matched user without checking whether that account

CVE-2026-91973 HIGH POC
8.7 Sep 15

Vikunja instances before 2.6.0 expose CalDAV BasicAuth endpoints (/dav, /.well-known, and /feeds) that are not covered b

CVE-2026-91972 HIGH POC
8.7 Sep 15

Vikunja versions before 2.6.0 ship authentication endpoints under /api/v2 (login, register, password-reset, and OAuth to

CVE-2026-91985 HIGH POC
8.7 Sep 15

Vikunja prior to 2.6.0 leaks the secret hash that backs a project's link shares through its single-share read endpoint,

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