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CVE-2026-61684 – Authentication Bypass and Cross-Tenant Data Disclosure – FastGPT 4.15.0-beta4

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Summary

CVE-2026-61684 is a high-severity authentication bypass vulnerability (CVSS 4.0: 8.8) affecting FastGPT, an open-source, self-hosted knowledge-based AI application platform developed by labring. The flaw stems from a hard-coded default credential used to sign JWTs that guard the platform’s plugin invoke endpoints — a misconfiguration present in virtually all default deployments — enabling unauthenticated remote attackers to perform cross-tenant user data disclosure and unauthorized file writes. The vulnerability is fixed in FastGPT version 4.15.0-beta5.

Technical details

  • Root cause: The plugin invoke reverse-call endpoints under /api/invoke/* authenticate requests solely by verifying a JWT signed with the environment variable INVOKE_TOKEN_SECRET. This secret defaults to the constant string token and was never configured in FastGPT’s official deployment templates (CWE-798: Use of Hard-coded Credentials), meaning the overwhelming majority of production deployments share an identical, publicly known signing key.
  • Trigger conditions: Any network-reachable FastGPT instance running version 4.15.0-beta4 with the default (or unset) INVOKE_TOKEN_SECRET value. No prior account, session, or other credential is required.
  • Attack vector: An unauthenticated remote attacker self-signs an HS256 JWT using the known secret (token) and submits it directly to the vulnerable endpoints.
  • Impact:
    • Cross-tenant PII disclosure: Calling /api/invoke/userInfo with attacker-supplied tmbId values returns personal information belonging to arbitrary tenants on the platform (CVSS 4.0 Confidentiality: High).
    • Unauthorized file writes: Calling /api/invoke/fileUpload allows the attacker to inject attacker-controlled content into chat files on the platform (CVSS 4.0 Integrity: Low).

Affected software

  • FastGPT (labring/FastGPT) version 4.15.0-beta4

Severity

  • CVSS 4.0 Base Score: 8.8 (High)
  • Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:L/VA:N/SC:N/SI:N/SA:N

Mitigation and recommended actions

  • Immediate — upgrade: Update FastGPT to version 4.15.0-beta5, which enforces proper INVOKE_TOKEN_SECRET configuration and addresses this vulnerability (fix introduced in PR #7170, commit f5f1e58).
  • If immediate upgrade is not possible:
    • Set a strong, randomly generated value for the INVOKE_TOKEN_SECRET environment variable in your deployment configuration to replace the insecure default.
    • Restrict network access to the /api/invoke/* endpoints at the firewall or reverse-proxy level, limiting reachability to only trusted internal systems.

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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