CVE-2026-56278: 
Flowise vulnerability analysis and mitigation

CVE-2026-56278 is an authentication bypass vulnerability in Flowise, an open-source LLM orchestration platform, caused by a weak hardcoded default session secret. Flowise versions 3.0.13 and earlier use the literal string 'flowise' as the default secret for the express-session middleware when the EXPRESS_SESSION_SECRET environment variable is not configured (packages/server/src/enterprise/middleware/passport/index.ts). Because this default is publicly visible in the source code, any unauthenticated attacker can forge valid signed session cookies to impersonate any user and bypass authentication entirely. The vulnerability was published on June 30, 2026, and carries a CVSS v3.1 score of 9.1 (Critical) and a CVSS v4.0 score of 9.3 (Critical) (Github Advisory, Flowise Advisory).

The root cause is classified as CWE-798 (Use of Hard-coded Credentials). The vulnerable code pattern is secret: process.env.EXPRESS_SESSION_SECRET || 'flowise' at line 55 of packages/server/src/enterprise/middleware/passport/index.ts, which falls back to the predictable string 'flowise' when the environment variable is absent. The .env.example file treats EXPRESS_SESSION_SECRET as optional (commented out), compounding the risk by implying that omitting it is acceptable in production. An attacker with knowledge of this default — trivially obtained from the public repository — can use standard Node.js express-session cookie-signing libraries to craft a valid, signed session cookie for any target user ID, requiring no prior credentials or user interaction (Flowise Advisory, Github Advisory).

Successful exploitation grants an unauthenticated remote attacker full authenticated access to the Flowise application, allowing them to perform any action available to the impersonated user — including accessing AI workflows, API keys, credentials stored within pipelines, and sensitive configuration data. The confidentiality and integrity of all data managed by the application are at high risk, as an attacker can read, modify, or delete workflows and connected integrations. Because Flowise commonly integrates with external LLM APIs, databases, and enterprise data sources, a compromised session could serve as a pivot point for broader lateral movement into connected systems (Github Advisory, Flowise Advisory).

1. Reconnaissance: Identify internet-facing Flowise instances (versions ≤3.0.13) using tools like Shodan or Censys, searching for Flowise-specific HTTP response headers or UI fingerprints.
2. Obtain the default secret: Retrieve the hardcoded default session secret 'flowise' from the publicly available Flowise source code on GitHub (packages/server/src/enterprise/middleware/passport/index.ts, line 55).
3. Identify a target user: Enumerate valid user session identifiers or user IDs through any unauthenticated endpoint, or target a known administrative account (e.g., default admin user).
4. Forge a signed session cookie: Using a Node.js script with the express-session and cookie-signature libraries, craft a session cookie signed with the secret 'flowise' that encodes the target user's session data (e.g., s:userId.<HMAC-SHA256 signature using 'flowise'>).
5. Submit the forged cookie: Send an HTTP request to the Flowise application with the forged connect.sid cookie in the Cookie header.
6. Achieve authenticated access: The server validates the cookie signature using the default secret, accepts the session as legitimate, and grants full authenticated access as the impersonated user — enabling data exfiltration, workflow manipulation, or credential theft (Flowise Advisory, Github Advisory).

• Network: Unexpected authenticated API requests (e.g., to /api/v1/ endpoints) originating from IP addresses with no prior login history; high-frequency requests to authenticated endpoints without a preceding login flow.
• Logs: Application access logs showing authenticated session activity where no corresponding login event exists in authentication logs; session cookies with the connect.sid prefix appearing from unusual geographic locations or IP ranges.
• Application Behavior: Unauthorized modifications to AI workflows, chatflows, or API key configurations; unexpected creation, deletion, or export of pipelines or credentials.
• Configuration: Absence of the EXPRESS_SESSION_SECRET environment variable in the Flowise server configuration, confirming the default secret is in use.

The primary remediation is to upgrade Flowise to version 3.1.0 or later, which addresses this vulnerability (Github Advisory). For deployments that cannot immediately upgrade, set the EXPRESS_SESSION_SECRET environment variable to a cryptographically strong, randomly generated value of at least 256 bits before restarting the server — this immediately invalidates any cookies forged using the default secret. The Flowise advisory further recommends that the application be modified to throw a startup error if EXPRESS_SESSION_SECRET is not explicitly configured, preventing accidental use of the default in production (Flowise Advisory). After patching, conduct a security audit of session logs to identify any unauthorized access that may have occurred.

The vulnerability was discovered via a deep code scan by Kolega.dev and reported through FlowiseAI's security advisory process (Flowise Advisory). VulnCheck published an advisory highlighting the session hijacking risk (Github Advisory). A post on Bluesky from the CyberHub blog noted the vulnerability shortly after disclosure, indicating some community awareness, though broader media coverage has been limited given the lack of active exploitation.