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

CISA KEV is observed exploitation evidence. FIRST EPSS is a dated prediction of exploitation in the next 30 days. Missing scores are unknown. This collector requests predictions only for explicit CVE aliases in the public NuGet archive; Microsoft release views retain their existing prediction scope.

No collected risk observation for these identifiers. This does not establish absence of exploitation or a zero probability.

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.

Source published

9 Oct 2026 20:49:08 UTC

Source modified

13 Oct 2026 20:25:26 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: cve-program · CVE Program Terms of Use. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 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

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.

Source published

Oct 9, 2026, 8:49:08 PM (timezone not stated)

Source modified

Oct 13, 2026, 8:25:26 PM (timezone not stated)

Observed here

8 Nov 2026 01:58:38 UTC

Source terms

ENISA EUVD · source terms and attribution apply

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: euvd · ENISA EUVD · source terms and attribution apply. Source text is retained; field grouping and change labels are provided by ChangeIntel.

EUVD CVSS 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

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.

Source published

9 Oct 2026 21:17:05 UTC

Source modified

16 Oct 2026 20:04:29 UTC

Observed here

25 Oct 2026 14:19:28 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: nvd · NIST NVD usage terms; underlying source attribution retained. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 4.0 · [email protected] · Secondary · 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

## Summary With the per-provider OIDC `emailfallback` option enabled, Vikunja links an SSO login to a pre-existing **local** (username+password) account using only the `email` claim — no `email_verified` (or Microsoft `xms_edov`) check and no password check, on the unauthenticated callback. An attacker who can make the configured issuer emit a token bearing a victim's email logs in as that victim with a full session and no victim interaction (the nOAuth / Grafana CVE-2023-3128 class). The 2.3.0 fix for GHSA-8jvc-mcx6-r4cg added a TOTP gate, not an `email_verified` gate, so users without TOTP remain exposed. ## Details References are `pkg/modules/auth/openid/openid.go` at HEAD. Identity is first resolved on the immutable `(issuer, subject)` pair (`openid.go:428`). On a subject miss with `emailfallback` on, `fallbackSearchUsers` adds an email-only lookup against local accounts: ```go // openid.go:413 searches = append(searches, &user.User{Issuer: user.IssuerLocal, Email: cl.Email}) ``` `getUser` resolves this via `s.Get()`, which ANDs non-zero fields -> `WHERE issuer='local' AND email=?`. Local users always have `Issuer="local"` (`user_create.go:38`), so the lookup matches any local account by email alone; `getOrCreateUser` returns it and the caller mints a session — the password is never read. The `claims` struct has no `email_verified` field (`openid.go:80`) and `getClaims` never consults one; a repo-wide grep for `email_verified`/`xms_edov` returns nothing. The code already warns about this at `openid.go:388` ("Discouraged for untrusted providers where someone can set email without verification") — but enforces nothing. ## Impact Unauthenticated takeover of any existing **local** account (read/write/delete its projects, tasks, attachments, shares), bypassing the password. Scope notes: only `issuer='local'` accounts are matched (not pure-SSO users); the attacker's `sub` is not bound to the victim record, but the attack is repeatable; TOTP users are protected by the 2.3.0 `enforceTOTPIfRequired` gate (`openid.go:250`), non-TOTP users are not. ## Preconditions 1. Admin enabled `emailfallback: true` (defaults false — a default install is unaffected). 2. The configured issuer lets the attacker assert the victim's unverified email: a self-service IdP (Keycloak/Authentik/Auth0/Dex with editable email), a mixed federation, or a multi-tenant Entra `/common` app. `iss`/`aud` are pinned, but the attacker controls `email`, not the issuer. 3. The victim has a local account. Not reachable against a single-tenant IdP that verifies email and disallows self-set addresses. ## Recommended Fix Add `email_verified` to the `claims` struct and require it `true` on the email-fallback branch before linking to a local account; reject when absent/false. For Entra also require `xms_edov` and pin multi-tenant configs to an allowed-tenant list. Fail closed on an email collision not backed by a verified email from a trusted single-tenant issuer rather than silently logging the caller in.

Source published

9 Oct 2026 20:49:06 UTC

Source modified

19 Oct 2026 21:40:54 UTC

Observed here

24 Oct 2026 13:19:41 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V4 · 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

Publisher rating · HIGH

Vikunja: OIDC email-fallback account linking ignores email_verified, enabling local-account takeover in code.vikunja.io/api. NOTE: The source advisory for this report contains additional versions that could not be automatically mapped to standard Go module versions. (If this is causing false-positive reports from vulnerability scanners, please suggest an edit to the report.) The additional affected modules and versions are: code.vikunja.io/api from v1.0.0 before v2.4.0.

Source published

19 Oct 2026 21:08:26 UTC

Source modified

19 Oct 2026 21:31:49 UTC

Observed here

24 Oct 2026 13:19:41 UTC

Source terms

OSV · upstream source license applies

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · OSV · upstream source license applies. Source text is retained; field grouping and change labels are provided by ChangeIntel.