CVE-2026-63398

Received Received - Intake

SAML Authentication Bypass in Coop Review Tool

Publication date: 2026-10-30

Last updated on: 2026-10-30

Assigner: GitHub, Inc.

Description

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.

CVSS Scores

EPSS Scores

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Meta Information

Published

2026-10-30

Last Modified

2026-10-30

Generated

2026-10-31

AI Q&A

2026-10-31

EPSS Evaluated

N/A

NVD

CVE-2026-63398

Affected Vendors & Products

Vendor	Product	Version / Range
roostorg	coop	< 1.0.2

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-287	When an actor claims to have a given identity, the product does not prove or insufficiently proves that the claim is correct.

Attack-Flow Graph

Executive Summary

This vulnerability is a SAML-based cross-tenant account takeover in Coop, an open source review tool. It occurs when an attacker controls a SAML IdP signing key for one organization and submits a crafted assertion for a victim's email to another organization's SAML callback endpoint. The victim's email matches a user in the target organization, allowing the attacker to impersonate that user and gain full access without privileges in the target organization.

Impact Analysis

If you are a user of Coop, an attacker could gain unauthorized access to your account in another organization by exploiting this vulnerability. This could lead to data exposure, unauthorized actions, or further compromise of your account or the systems you interact with through Coop.

Compliance Impact

This vulnerability could lead to unauthorized access to sensitive data, violating confidentiality requirements in GDPR and HIPAA. Organizations using Coop may face compliance violations, data breaches, and potential legal consequences if this vulnerability is exploited to access protected health or personal information.

Mitigation Strategies

Upgrade Coop to version 1.0.2 or later to address the SAML strategy vulnerability. Ensure no organizations share SAML signing certificates with untrusted parties.

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