Rocket.Chat CVE-2026-58066

Requires the target Rocket.Chat instance to have SAML SSO enabled and configured to trust an external IdP certificate; the attacker must possess at least one document carrying a valid signature made by that trusted IdP certificate to reuse as the signature donor. Given CVSS PR:N/UI:N, no attacker authentication or user interaction is needed once a valid signed sample is available. Limiting factors: instances without SAML enabled are not affected at all, and obtaining a genuinely IdP-signed sample is the practical prerequisite (an attacker's own legitimate SAML login typically satisfies this). Affected versions are all releases below the per-branch fixes (e.g., <8.7.0, <8.6.1 ... <7.10.14).

This is a genuine high-priority issue, not an inflated CVSS number. The supplied CVSS 3.0 vector AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H (9.8) is internally consistent with the description: SAML endpoints are network-reachable, no attacker authentication is needed (the whole point is impersonating any account), and the attacker only needs one valid IdP-signed document as a signature donor plus the ability to craft the wrapper - low complexity. Classic SAML XSW bypasses are highly reliable and scriptable once a signed sample is obtained, so real-world exploitability is high where SAML SSO is enabled. No EPSS score, KEV status, or SSVC decision data was provided, so exploitation-probability and automatable ratings cannot be quantified from the input; the absence of KEV means active exploitation is not confirmed. The main real-world limiter is configuration scope: only deployments that have SAML SSO enabled and trust an external IdP are affected - instances using only password or OAuth login are not exposed.

An attacker obtains any single SAML response legitimately signed by the target's trusted IdP certificate - for example their own valid login, an intercepted assertion, or a leaked sample - and wraps it so the genuine signature stays valid while forged NameID/attribute values identifying an admin account are placed where Rocket.Chat reads identity. Submitting this crafted document to the SAML ACS endpoint authenticates the attacker as the impersonated administrator without any password. No weaponized exploit is public, but the patch's regression tests (samlResponseNestedInWrapper) demonstrate the exact wrapping technique.