Siderolabs Omni CVE-2026-45720

Summary

SAML.getSession (internal/pkg/auth/interceptor/saml.go) checks the Used flag on a SAMLAssertion resource and then marks it used in two separate state operations. Because the check and the update are not atomic, concurrent requests carrying the same saml-session token can both observe Used == false, both pass validation, and both return a successful authentication context. An attacker who obtains a valid saml-session token can exploit this window to authenticate as the token's owner multiple times, defeating the one-time-use guarantee.

Severity

• Attack Vector: Local: the attacker needs to either be able to intercept the local, unencrypted traffic or needs access to user's browser.
• Attack Complexity: High: the attacker must first obtain a valid saml-session token belonging to the victim (requires a separate interception step; the token is ephemeral and single-use by design).
• Privileges Required: None: no Omni account is required to carry out the race once the session token is in hand.
• User Interaction: Required: the victim must initiate a SAML authentication flow to produce the session token that the attacker intercepts.
• Scope: Unchanged: the impact stays within Omni's authorization boundary.
• Confidentiality Impact: High: successful exploitation authenticates the attacker as the victim's email identity, granting read access to any resource accessible to that identity.
• Integrity Impact: High: the attacker can confirm one or more public keys under the victim's identity (via ConfirmPublicKey), establishing persistent access credentials tied to the victim's account.
• Availability Impact: High: if the attacker can successfully perform the attack and if the victim is a privileged Omni user, e.g., an Omni Operator or Admin, they can take Omni down.

Impact

• Session replay: A stolen saml-session token can be used more than once, defeating its single-use guarantee.
• Multiple public key confirmations: An attacker who steals the session can confirm N attacker-controlled public keys under the victim's identity in a single stolen session window, creating N persistent long-lived API credentials tied to the victim's account.
• Authentication as victim: Any gRPC endpoint gated by the SAML interceptor can be reached as the victim's email identity during the race window.
• Audit log pollution: Each raced call generates an audit entry attributed to the victim's email, obscuring the attacker's actions.

Credit

This vulnerability was discovered and reported by bugbunny.ai.