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CVE-2026-56278 – Authentication Bypass via Hardcoded Session Secret – Flowise ≤ 3.0.13

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Summary

CVE-2026-56278 is a critical authentication bypass vulnerability in Flowise, the open-source AI workflow and LLM-agent builder. The flaw stems from a hardcoded default express-session secret ('flowise') that is used when the EXPRESS_SESSION_SECRET environment variable is not configured — a condition common in default and quick-start deployments. Because this secret is publicly visible in the source code, any unauthenticated remote attacker can forge cryptographically valid session cookies to impersonate any user, including administrators, without credentials. The vulnerability carries a CVSS 4.0 score of 9.3 (Critical).

Technical details

  • Root cause: The express-session middleware in packages/server/src/enterprise/middleware/passport/index.ts (line 55) uses the fallback secret: process.env.EXPRESS_SESSION_SECRET || 'flowise'. When EXPRESS_SESSION_SECRET is unset, the hardcoded string 'flowise' — publicly visible in the repository — is used to HMAC-sign all session cookies.
  • Trigger condition: Any Flowise instance deployed without explicitly setting the EXPRESS_SESSION_SECRET environment variable is vulnerable. This includes the default Docker and npm quick-start configurations.
  • Attack vector: An attacker with network access to the Flowise web interface crafts a session cookie offline using the known secret 'flowise', signing it with the standard HMAC-SHA256 express-session algorithm. The forged cookie is then submitted to the target instance, which accepts it as legitimate.
  • No authentication or interaction required: The attack is fully unauthenticated and requires no user interaction. CVSS 4.0 vector AV:N/AC:L/AT:N/PR:N/UI:N confirms network-reachable, zero-complexity, zero-privilege exploitation.
  • Impact: Full authentication bypass. A successful attacker gains complete access to all Flowise workflows, LLM configurations, stored credentials, API keys, and any data managed by the platform (CVSS 4.0: VC:H/VI:H).
  • CWE: CWE-798 – Use of Hard-coded Credentials.

Affected software

  • Flowise (npm package flowise) versions ≤ 3.0.13
  • Fixed in Flowise 3.1.0

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: Update Flowise to version 3.1.0 or later, which removes the hardcoded fallback and enforces explicit configuration of the session secret.
  • If immediate patching is not possible:
    • Set the EXPRESS_SESSION_SECRET environment variable to a cryptographically strong, randomly generated value (minimum 256 bits / 32 bytes) in all Flowise deployment configurations before restarting the service.
    • Restrict network access to the Flowise web interface to trusted IP ranges or place it behind an authenticated reverse proxy.
    • Audit session logs for any anomalous or unexpected authenticated sessions, which may indicate prior exploitation.

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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