OpenBao permits an attacker to launch an OIDC authentication request using the direct callback mode without any user confirmation. An attacker can construct a URL that, when a victim visits it, automatically completes the login flow and issues a bearer token directly to the attacker. The compromised token grants the attacker full privileges of the victim user within the OpenBao system. This vulnerability is a classic remote phishing scenario and represents a failure in authentication flow design, corresponding to the CWE-384 weakness in missing user confirmation for sensitive operations.

The flaw exists in all OpenBao deployments using versions earlier than 2.5.2 that configure any role with callback_mode set to direct. Versions 2.5.2 and later introduce a mandatory confirmation prompt for direct callback logins, thereby mitigating the vulnerability. Operations that rely on direct OIDC callbacks in older releases are therefore exposed.

The CVSS score of 9.6 indicates a very high impact, although the EPSS score of under 1% suggests that exploitation is presently uncommon. Attackers only need to supply a crafted link and persuade a target user to click it; no additional code execution or privileged access is required. Because the flaw uses the OpenBao token issuer itself, successful exploitation results in immediate access to the victim’s session. Although the vulnerability is not yet listed in the CISA KEV catalog, its high severity and low overhead for attackers still pose a significant risk to any OpenBao instance still running a vulnerable version or retaining direct callback roles.