CVE-2026-4525 is a high-severity vulnerability in HashiCorp Vault that causes Vault tokens to be forwarded to external authentication plugin backends when specific header pass-through configurations are active. Organizations using Vault to manage secrets, credentials, or privileged access are at risk of token exposure to any system or party with access to those plugin backends. Exploitation could allow an attacker to move laterally through Vault-protected infrastructure or escalate privileges across systems that rely on Vault for authentication.