TokenMix Research Lab · 2026-04-29
Flowise MCP RCE: 10 Fixes for CVE-2026-40933 and Upsonic
Last Updated: 2026-04-29
Author: TokenMix Research Lab
Flowise MCP RCE is no longer a theoretical protocol debate. CVE-2026-40933 gives Flowise a critical authenticated RCE path through MCP adapters, and Upsonic CVE-2026-30625 shows the same failure mode in another agent framework.
The short version: patch Flowise to 3.1.0 or later, patch Upsonic to 0.72.0 or later, and do not treat input sanitization as the control boundary for MCP STDIO. Based on the GitHub Advisory Database entry for CVE-2026-40933, Flowise versions up to 3.0.13 are affected and 3.1.0 is patched. Based on Snyk's Upsonic advisory, Upsonic versions before 0.72.0 are affected. OX Security's April 27 analysis says both projects tried to reduce risk through sanitization, but argument-level execution behavior still bypassed that approach.
For the broader MCP threat background, read TokenMix.ai's MCP security flaw guide and MCP protocol guide. This article is the patch-focused version for teams running Flowise, Upsonic, or similar MCP-enabled agent servers.
Table of Contents
- Quick Verdict
- Why This Topic Has Ranking Potential
- What Actually Broke
- Affected Versions and Patch Status
- The 10 Controls That Matter
- Priority Matrix for Production Teams
- Cost and Blast Radius Math
- How to Hardening-Test an MCP Deployment
- Related Articles
- FAQ
- Sources
Quick Verdict
Flowise CVE-2026-40933 is a patch-now issue. Upsonic CVE-2026-30625 is a patch-now issue. The broader lesson is stronger: MCP STDIO should be treated as process execution, not a harmless plugin configuration.
| Question | Short answer | Confidence |
|---|---|---|
| Is Flowise affected? | Yes, Flowise and flowise-components up to 3.0.13 are affected; 3.1.0 is patched per GitHub Advisory Database. | High |
| Is Upsonic affected? | Yes, versions before 0.72.0 are affected per Snyk. | High |
| Is this only a Flowise bug? | No. OX frames it as an MCP supply-chain pattern around STDIO command execution. | High |
| Is input sanitization enough? | No. OX's follow-up shows sanitization can be bypassed through allowed command arguments. | High |
| Should public MCP admin UIs stay online? | No. Put them behind authentication, network controls, and audit logging. | High |
Why This Topic Has Ranking Potential
The best SEO target here is not broad "MCP security." That keyword is already crowded. The better target is the incident cluster: Flowise MCP RCE fix, CVE-2026-40933 patch, Upsonic CVE-2026-30625, MCP STDIO sanitization bypass, and AI agent server hardening.
| Hotspot | Search intent | Competition | Why it can rank |
|---|---|---|---|
| GPT-5.5 / Spud | Broad model news, pricing, benchmarks | High | TokenMix already has several GPT-5.5 pages. |
| DeepSeek V4 | Model review, API pricing, open weights | High | TokenMix already covers V4 deeply. |
| MCP RCE broad story | News and protocol-risk explainer | Medium-high | TokenMix already has a broad MCP security article. |
| Flowise CVE-2026-40933 fix | Patch guide, affected versions, remediation | Low-medium | Fresh, specific, high urgency. |
| Upsonic CVE-2026-30625 | Patch guide, MCP task hardening | Low | Sparse coverage and strong security intent. |
TokenMix.ai's read: the highest-probability page is a specific fix guide, not another news recap. Developers searching CVE numbers are usually closer to action. They want versions, controls, and a checklist.
What Actually Broke
The bug class is direct input-to-process execution through MCP STDIO configuration. That phrase matters. STDIO MCP servers are not just data connectors. They can start local or server-side processes.
According to the Flowise GitHub advisory, the Flowise issue sits in Custom MCP configuration: an authenticated user can add an MCP stdio server with arbitrary command behavior. The patched version is 3.1.0. According to Snyk's Upsonic advisory, Upsonic before 0.72.0 is vulnerable through MCP server task creation.
The key twist is that the vulnerable systems were not doing nothing. OX's April 27 write-up says Flowise and Upsonic attempted command filtering and special-character restrictions, but allowed command arguments could still reach OS-level execution paths.
| Layer | What teams thought it did | What failed | Safer interpretation |
|---|---|---|---|
| UI authentication | Keeps random outsiders away | Authenticated users can still be attackers or compromised accounts | Necessary, not sufficient |
| Command allowlist | Allows only known binaries | Allowed binaries can receive dangerous arguments | Treat args as code-adjacent |
| Special-character filtering | Blocks obvious shell chains | Execution can happen without obvious separators | Not a security boundary |
| MCP STDIO | Plugin transport | Process-launch surface | Sandbox and govern it |
| Agent workflow | Productivity layer | Privileged automation path | Needs AppSec controls |
Affected Versions and Patch Status
Use this table as the first production triage pass.
| Product | CVE | Affected versions | Fixed version / mitigation | Source |
|---|---|---|---|---|
| Flowise | CVE-2026-40933 | Flowise up to 3.0.13 | Upgrade to Flowise 3.1.0 or later | GitHub Advisory |
| flowise-components | CVE-2026-40933 | flowise-components up to 3.0.13 | Upgrade to 3.1.0 or later | GitHub Advisory |
| Upsonic | CVE-2026-30625 | Versions before 0.72.0 | Upgrade to 0.72.0 or later | Snyk |
| LiteLLM | CVE-2026-30623 | 1.74.2 to before 1.83.7 | Upgrade to 1.83.7 or later | Snyk LiteLLM advisory |
| Windsurf | CVE-2026-30615 | Reported by OX as prompt-injection to MCP config RCE | Check vendor update status before using MCP with untrusted content | OX full advisory |
This is a live security area. Version numbers above reflect public advisories available on April 29, 2026. Re-check vendor advisories before freezing a production exception.
The 10 Controls That Matter
The fix is not "add a regex." The fix is to stop treating MCP STDIO as a trusted configuration field.
| # | Control | Why it matters | Priority |
|---|---|---|---|
| 1 | Patch Flowise and Upsonic immediately | Removes known vulnerable code paths | P0 |
| 2 | Disable Custom MCP STDIO by default | Eliminates the risky transport path for most users | P0 |
| 3 | Put MCP admin UIs behind SSO and network allowlists | Reduces exposed attack surface | P0 |
| 4 | Run MCP servers in isolated containers or sandboxes | Limits file, network, and credential access after compromise | P0 |
| 5 | Deny arbitrary command and args fields | Prevents user-controlled process launch | P0 |
| 6 | Use per-user RBAC for agent tool creation | Stops normal users from adding privileged tools | P1 |
| 7 | Separate agent runtime secrets from admin secrets | Limits API-key loss if the runtime is compromised | P1 |
| 8 | Log MCP server creation, edits, and process starts | Makes incident response possible | P1 |
| 9 | Use a private registry for approved MCP tools | Reduces package and marketplace supply-chain risk | P1 |
| 10 | Add runtime egress controls | Blocks reverse shells, data exfiltration, and crypto-mining paths | P1 |
The official MCP security best practices already emphasize authorization, session handling, scope minimization, and token handling. The Flowise/Upsonic lesson adds a practical rule: if an MCP feature can launch a process, it needs the same controls you would apply to a CI runner or plugin execution host.
Priority Matrix for Production Teams
If you run Flowise or Upsonic internally, treat this as a two-hour triage followed by a two-day hardening sprint.
| Environment | Exposure | First action | Follow-up |
|---|---|---|---|
| Public Flowise UI | High | Remove public access and patch to 3.1.0+ | Review all Custom MCP entries |
| Internal Flowise with many users | High | Patch and restrict MCP creation to admins | Add audit logs and RBAC |
| Upsonic agent framework | High | Patch to 0.72.0+ | Review MCP tasks for process execution |
| LiteLLM with MCP preview endpoints | Medium-high | Patch to 1.83.7+ | Disable unused MCP management endpoints |
| Local developer MCP setup | Medium | Remove untrusted MCP configs | Separate work and personal credentials |
| Read-only HTTP MCP servers | Lower | Verify auth and scopes | Add request logging and egress limits |
This is where many teams underreact. Internal does not mean safe. Agents usually hold API keys, repository access, cloud tokens, database credentials, or vector database credentials. A private agent server with weak MCP controls can be more valuable than a public marketing site.
Cost and Blast Radius Math
Security pages rank better when they answer the operator's real question: "How bad is this for my environment?" Use these formulas for an MCP security checklist review without inventing fake breach costs.
| Risk calculation | Formula | What it tells you |
|---|---|---|
| Estimated remediation hours | (MCP hosts x 2) + (workspaces x 0.5) + (public admin UIs x 1) |
First-pass patch, config review, and access lockdown effort |
| Secret rotation scope | runtime secrets + provider API keys + database credentials + vector DB tokens |
How much work starts if compromise is suspected |
| Blast radius score | public MCP admins + writable repos + reachable secret stores + outbound internet paths |
Whether this is a local issue or a platform incident |
| Runtime isolation gap | MCP tools with process execution - sandboxed MCP tools |
How many servers still need container or VM isolation |
The formula is intentionally simple. It is not a compliance model. It is a fast way to decide whether the incident is a one-host patch or a platform-wide agent server hardening sprint.
Scenario 1: Small Team
| Assumption | Value |
|---|---|
| Developers with access | 8 |
| MCP-enabled agent servers | 2 |
| API keys reachable from runtime | 6 |
| Time to patch and review | 4 hours |
| Time to recover from leaked keys | 1-2 days |
For a small team, the estimated cost is mostly engineering time. The remediation formula gives (2 hosts x 2) + (1 workspace x 0.5) + (1 public admin UI x 1) = 5.5 hours before secret review. That is still cheaper than a full key rotation, GitHub audit, and cloud log search after a suspected command injection incident.
Scenario 2: Agency or SaaS Team
| Assumption | Value |
|---|---|
| Client workspaces | 20 |
| Agent servers or builders | 5 |
| Secrets per workspace | 5-20 |
| If compromised | Cross-client exposure risk |
| Best control | Tenant-isolated runtime + private MCP registry |
The agency risk is not only RCE. It is cross-client blast radius. A conservative secret rotation scope is 20 workspaces x 5 secrets = 100 credentials at the low end. One compromised Flowise or Upsonic host can expose multiple customer API keys if runtime secrets are shared.
Scenario 3: Enterprise AI Platform
| Assumption | Value |
|---|---|
| Internal MCP tools | 50+ |
| Agent users | 500+ |
| Registry sources | Multiple |
| Admin UI exposure | Often wider than intended |
| Best control | Central policy gateway + egress monitoring |
At enterprise scale, the hardening job is governance. If only 20% of 50 internal MCP tools can launch local processes, the runtime isolation gap is 10 tools. A single patch does not solve unreviewed MCP tool sprawl. TokenMix.ai's recommendation is to inventory MCP servers the same way you inventory production APIs.
How to Hardening-Test an MCP Deployment
Do not test this by running public exploit payloads. Test the controls.
| Test | Expected safe result |
|---|---|
| Can a normal user create a Custom MCP STDIO server? | No |
| Can any MCP config include arbitrary command and args fields? | No |
| Can the runtime read production API keys by default? | No |
| Can the MCP runtime reach the public internet freely? | No |
| Are MCP config changes logged with user identity and timestamp? | Yes |
| Are approved MCP tools pinned by source and version? | Yes |
| Is every public MCP admin UI behind SSO or VPN? | Yes |
| Can you rotate agent runtime credentials in under 30 minutes? | Yes |
If the answer is wrong on the first four tests, patching alone is not enough. You still have a process-execution surface exposed to agent workflows.
Related Articles
- MCP Security Flaw: 150M Installs at Risk from STDIO Exploit
- MCP Protocol 2026: 97M Downloads, 10K Servers, Why It's Winning
- MCP Servers List 2026: Complete Directory of 70+ Production Servers
- LLM Security News 2026: Latest Attacks, Defenses & Updates
- API Error Troubleshooting Directory: OpenAI, Anthropic, Cursor Fixes
FAQ
What is the Flowise MCP RCE vulnerability?
Flowise CVE-2026-40933 is an authenticated remote code execution vulnerability in MCP adapter handling. The GitHub advisory says Flowise and flowise-components up to 3.0.13 are affected, with 3.1.0 listed as patched.
How do I fix CVE-2026-40933 in Flowise?
Upgrade Flowise and flowise-components to 3.1.0 or later. Then review Custom MCP configurations, restrict MCP creation to trusted admins, and remove public access to Flowise admin surfaces.
What is Upsonic CVE-2026-30625?
Upsonic CVE-2026-30625 is an arbitrary code injection issue tied to MCP server task creation. Snyk says affected versions are before 0.72.0 and recommends upgrading to 0.72.0 or higher.
Is input sanitization enough for MCP STDIO?
No. OX's Flowise/Upsonic analysis shows that sanitization and approved command lists can still be bypassed through command arguments. Treat STDIO as process execution and isolate it accordingly.
Is this a problem with MCP itself or only with Flowise?
Both layers matter. Flowise and Upsonic have concrete patched CVEs, but OX describes the broader issue as an MCP STDIO supply-chain pattern. Any product that lets users configure STDIO commands needs strict controls.
Should I disable MCP entirely?
Not necessarily. Disable Custom MCP STDIO where it is not needed, keep approved MCP tools, and run them inside isolated runtimes. MCP is useful, but it should not get unchecked process-launch privileges.
What is the best immediate checklist?
Patch affected packages, remove public admin access, disable arbitrary STDIO configuration, rotate exposed runtime secrets if compromise is suspected, and add logs for MCP server creation and edits.
How does TokenMix.ai fit into MCP security planning?
TokenMix.ai is not a security scanner. The relevant architecture point is routing: keep AI model access behind one controlled API layer, separate model keys from agent runtime secrets, and avoid spreading provider credentials across every MCP server.