Critical 9.6 CVSS OIDC Flaws in OpenBao Turn “Direct Login” Into a Phishing Trap

The OpenBao community, the open-source initiative dedicated to managing and distributing sensitive data like secrets and certificates, has released a high-priority security update. Two significant vulnerabilities in the platform’s OIDC/JWT authentication flow have been identified, including a critical “remote phishing” risk and a dangerous Cross-Site Scripting (XSS) flaw.

Both vulnerabilities center on a specific configuration known as callback_mode=direct, which streamlines the login process but, as it turns out, creates a significant opening for attackers.

The most severe of the two flaws, tracked as CVE-2026-33757, carries a CVSS score of 9.6, placing it in the “Critical” category.

When OpenBao is configured for OIDC direct callback mode, it fails to prompt for user confirmation during the login process.

An attacker can initiate an authentication request and trick a victim into visiting a specific URL. Because the “direct” mode bypasses manual confirmation, the victim is automatically logged into the attacker’s session.

The attacker can then poll the OpenBao API for a token until it is issued, effectively hijacking the authentication flow despite it being based on standard authorization code principles.

The second vulnerability, tracked as CVE-2026-33758 (CVSS 9.4), involves a Reflected Cross-Site Scripting (XSS) weakness within the OpenBao Web UI. Systems using callback_mode=direct are susceptible to XSS through the error_description parameter on failed authentication pages.

If an attacker successfully executes this script, they could gain direct access to the authentication token used by a victim in the Web UI. OpenBao developers have addressed this by replacing the dynamic error_description parameter with a static, non-exploitable error message.

The OpenBao community has released Version 2.5.2, which introduces a mandatory confirmation screen for direct-type logins to ensure manual user interaction.

If you cannot upgrade immediately, security teams should consider the following mitigations:

• Disable Direct Mode: Remove any roles currently configured with callback_mode=direct.
• Enforce Issuer Confirmation: Configure your OIDC token issuer to require manual confirmation for every session associated with the OpenBao Client ID.