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CVE-2026-58122 – Authentication Bypass – Hermes WebUI before 0.51.307

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Summary

CVE-2026-58122 is a critical authentication bypass vulnerability in Hermes WebUI (nesquena/hermes-webui), an AI agent web interface commonly deployed internet-facing. By supplying a spoofed loopback address in the X-Forwarded-For HTTP header, unauthenticated remote attackers can circumvent local-origin IP restrictions enforced on onboarding endpoints, enabling server-side request forgery, LLM configuration hijacking, and persistent OAuth token theft. All versions prior to 0.51.307 are affected, and the vulnerability carries a CVSS 4.0 score of 9.3 (Critical).

Technical details

  • Root cause: The application improperly trusts the client-supplied X-Forwarded-For HTTP header when evaluating IP-based access controls on sensitive onboarding endpoints. By setting this header to a loopback address (e.g., 127.0.0.1 or ::1), an unauthenticated remote attacker can impersonate a local-origin request and gain access to restricted onboarding functionality (CWE-348: Use of Less Trusted Source).
  • Trigger conditions: The affected onboarding endpoints are reachable over the network on a standard Hermes WebUI deployment. No authentication, prior user interaction, or elevated privileges are required — a single crafted HTTP request is sufficient.
  • Attack vector: Network-accessible; exploitation requires only the addition of a spoofed X-Forwarded-For header to an HTTP request targeting the onboarding API.
  • Impact:
    • Server-Side Request Forgery (SSRF): The bypass enables SSRF against internal services, including cloud metadata endpoints (e.g., AWS IMDSv1, GCP instance metadata), allowing attackers to harvest cloud credentials from the deployment environment.
    • LLM configuration hijack: Attackers can overwrite LLM provider configuration and API keys with attacker-controlled values, achieving persistent interception or manipulation of all AI interactions processed by the instance.
    • Persistent OAuth access: Attackers can initiate OAuth device-code flows to obtain persistent access tokens, which are stored in auth.json and provide long-term unauthorized access to the deployment.

Affected software

  • Hermes WebUI (nesquena/hermes-webui) — all versions prior to 0.51.307

Severity

CVSS 4.0 base score 9.3 (Critical)
Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N

Mitigation and recommended actions

  • Immediate: Upgrade to Hermes WebUI v0.51.307 or later. This release (commit 70596e6, PR #3764, published June 7, 2026) patches the onboarding endpoint spoofing vulnerability.
  • If immediate patching is not feasible: Restrict network-level access to the onboarding API endpoints via firewall rules or reverse-proxy configuration, permitting requests only from verified trusted internal IP ranges. Do not rely solely on application-layer IP checks as a security control.

IONIX Status

The IONIX research team is tracking ongoing exploitation attempts and recommends immediate patching. Potentially affected assets are outlined in this post.

References

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