GHSA-5x9f-6vg5-qg4m Omni has a TOCTOU race condition that allows multiple concurrent uses of a single-use SAML session token

• Go github.com/siderolabs/omni: < 1.6.6 → fixed in 1.6.6 • Go github.com/siderolabs/omni: >= 1.7.0, < 1.7.3 → fixed in 1.7.3

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.