CVE-2026-53515 in Better Auth
Summary
by MITRE • 07/15/2026
Better Auth is an authentication and authorization library for TypeScript. From 1.2.10 until 1.6.11, the @better-auth/sso plugin's POST /sso/register endpoint lets any organization member attach a new SSO provider to that organization because registerSSOProvider checks only for a membership row and does not require an owner or admin role, allowing attacker-controlled OIDC or SAML providers to drive /sso/callback/{providerId} organization provisioning. This issue is fixed in version 1.6.11.
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Analysis
by VulDB Data Team • 07/15/2026
The vulnerability exists within the @better-auth/sso plugin of the Better Auth authentication library, specifically affecting versions 1.2.10 through 1.6.11. This represents a critical authorization flaw that allows unauthorized users to escalate their privileges by attaching malicious SSO providers to organizations they belong to. The core issue stems from insufficient access controls within the registerSSOProvider function which only validates user membership status without enforcing role-based permissions.
The technical implementation flaw resides in how the POST /sso/register endpoint processes requests for adding SSO providers to organizations. The system performs a membership check but fails to validate whether the requesting user holds administrative or owner privileges within the target organization. This design oversight creates a path where any member can provision new identity providers, effectively bypassing intended security boundaries. When an attacker successfully registers a malicious OIDC or SAML provider through this endpoint, they can manipulate the /sso/callback/{providerId} flow to provision organizations under their control.
The operational impact of this vulnerability is severe and multifaceted. Attackers can leverage this flaw to gain unauthorized access to organizational resources by registering malicious identity providers that redirect users to attacker-controlled endpoints. This enables credential harvesting, privilege escalation, and potential lateral movement within the organization's digital infrastructure. The vulnerability essentially transforms any organization member into a potential attacker with elevated privileges, as they can control which SSO providers are available for use within their organization.
This issue aligns with CWE-284 (Improper Access Control) and represents a classic case of insufficient authorization validation. From an ATT&CK perspective, this vulnerability maps to T1078 (Valid Accounts) and T1531 (Account Access Removal) as it allows attackers to leverage legitimate user accounts to gain unauthorized access to organizational resources. The flaw also relates to T1098 (Account Manipulation) since attackers can modify account configurations through the SSO registration process.
Organizations should immediately implement mitigations including updating to version 1.6.11 or later, which resolves the authorization check issue. Additional defensive measures include monitoring SSO provider registration activities, implementing strict access controls for SSO configuration endpoints, and conducting regular security audits of identity provider configurations. Network-based detection should monitor for unusual patterns in SSO registration requests and callback endpoint usage to identify potential exploitation attempts.
The vulnerability demonstrates the critical importance of proper role-based access control implementation in authentication systems. It highlights how seemingly minor authorization checks can create significant security risks when omitted from critical administrative functions. Organizations relying on this library must ensure all SSO provider management operations enforce appropriate administrative privileges and maintain comprehensive audit trails of configuration changes to prevent similar issues in other components of their identity infrastructure.