Vikunja: OIDC email-fallback account linking ignores email_verified, enabling local-account takeover

published 2026-10-09 30 d ago modified 2026-10-19 20 d ago also GHSA-xv7q-fvmc-jx96 , GO-2026-6758 , EUVD-2026-95993

cvss: 7.5; version 4.0, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.1%; EPSS 0.1% chance of exploitation in 30 days, percentile 0%
public exploits: 0; none known

Vikunja is an open-source self-hosted task management platform. In versions 1.0.0 through 2.3.0, when an administrator enables the per-provider `emailfallback` option on an OpenID Connect provider, Vikunja links an SSO login to a pre-existing local (username+password) account using only the `email` claim from the IdP. The fallback never checks an `email_verified` (or Microsoft `xms_edov`) signal and never requires the matched account's password. An attacker who can obtain a token from the configured issuer carrying a victim's email logs in as that victim with a full session, with no consent or interaction from the victim. Version 2.4.0 fixes the issue.

Patch / fix

fixed in 1 links 2

go code.vikunja.io/api 2.4.0

github.com/go-vikunja/vikunja@7854f27 commit
github.com/go-vikunja/vikunja/releases/tag/v2.4.0 release

CISA SSVC

Exploitation: none
Automatable: no
Technical impact: total
Assessed: 26 d ago (2026-10-13)

Exploit prediction

0.09% chance of exploitation in the next 30 days, higher than 0% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by	version	score	vector
CNA	4.0	7.5	CVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
CNA	4.0	7.5	CVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Affected packages

ecosystem	package	affected	fixed in
go	code.vikunja.io/api	>=1.0.0, <2.4.0 all versions	2.4.0

Affected products

go-vikunja vikunja

Classification

Weakness

CWE-287 Improper Authentication
CWE-290 Authentication Bypass by Spoofing
CWE-345 Insufficient Verification of Data Authenticity

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

Summary