CVE-2026-63398CWE-287

Coop has SAML cross-tenant authentication bypass

High · published October 30, 2026

CVSS v4.0
7.4
EPSS
—
In the wild
Unconfirmed
What it is

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.

The record
Technical detail
CVSS v4.0
7.4 · HIGH
Vector
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
EPSS
Not scored
Weakness
CWE-287 · Improper Authentication
Published
2026-10-30T22:44Z
Timeline
  • 30 OCT 22:44Z
    Coop has SAML cross-tenant authentication bypass
    cvelistv5
  • 30 OCT 22:44Z
    Coop has SAML cross-tenant authentication bypass
    cvelistv5