Hermes WebUI before 0.51.307 contains a flaw that allows attackers to bypass authentication by sending a forged X-Forwarded-For header containing a loopback address, thereby circumventing the local‑origin IP restriction on onboarding endpoints. Once authentication is bypassed, attackers can perform server‑side request forgery against internal services, overwrite LLM provider configuration and API keys with attacker‑controlled values, or initiate OAuth device‑code flows to obtain persistent access tokens stored in auth.json. The vulnerability poses a significant threat to confidentiality, integrity, and availability by enabling remote attackers to manipulate internal configurations and persistently access data without proper authorization.

The flaw affects all Hermes WebUI installations produced by developer nesquena running any release prior to 0.51.307. No specific sub‑versions are listed beyond the upper bound; any pre‑0.51.307 build inherits the vulnerability.

The CVSS score of 9.3 denotes a high‑severity remote exploitation risk. The EPSS score of <1% indicates a very low but non‑zero exploitation probability, and the vulnerability is not listed in CISA's KEV catalog. Attackers can exploit the flaw via standard HTTP requests to the onboarding endpoints, given network reachability to the Web UI; they can then manipulate internal services and persistently gain access by modifying auth.json or overriding LLM configuration. The absence of local‑origin IP validation allows the spoofed X-Forwarded‑For header to bypass network restrictions, expanding the attack surface.