# CVE-2026-63398: Coop has SAML cross-tenant authentication bypass

Status: published. Published: 2026-10-30. Updated: 2026-11-02.

Coop is an open source review and moderation tool from ROOST. Prior to 1.0.2, the SAML strategy's verify callback resolved the authenticated user by email alone using `kyselyUserFindByEmail`, without binding the lookup to the organization in `/saml/login/:orgId/callback`. An attacker who administers an organization and controls its SAML IdP signing key can submit an assertion for a victim email to another organization's callback when that target organization has registered the same signing certificate. The assertion verifies against the target certificate, and the email resolves to the target user, creating a session as that user and allowing full cross-tenant account takeover without privileges in the target organization. Exploitation requires the unusual configuration in which the target certificate matches a signing key controlled by the attacker. This issue is fixed in version 1.0.2.

## Remediation

No remediation reported in collected sources

## Affected products and versions

- roostorg / coop: < 1.0.2 (affected). Source: CNA: GitHub_M

## Severity and prioritization

- CVSS 4.0: 7.4 (high); CVSS:4.0/AV:N/AC:L/AT:P/PR:H/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N; source: CNA: GitHub_M

- CISA KEV: No listing in collected sources

- EPSS: 0.18% as of 2026-11-02; percentile 8.00%

- SSVC: exploitation none; automatable no; technical impact total; source ADP: CISA-ADP

- Weaknesses: CWE-287

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://github.com/roostorg/coop/security/advisories/GHSA-2v93-383c-9fw2 (CNA: GitHub_M; x_refsource_CONFIRM)

- https://github.com/roostorg/coop/pull/783 (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/roostorg/coop/commit/d1be81b6b33abc1162ee6b9952d4bd1ca761b071 (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/roostorg/coop/releases/tag/1.0.2 (CNA: GitHub_M; x_refsource_MISC)

## Provenance

- CNA: GitHub_M: https://www.cve.org/CVERecord?id=CVE-2026-63398; retrieved 2026-11-02; source updated 2026-11-02

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-63398; retrieved 2026-11-02; source updated Not reported

Revision: 668b817f113585ca3620efea6e2d739586eafa48812fc57c11a36f8637dba5a1

Canonical: https://y2.dev/cve/CVE-2026-63398

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