Langflow Custom Component Sandbox Bypass Leading to Remote Code Execution
First seen Aug 29, 2026 · Updated Aug 29, 2026 · CVSS 9.9
A critical flaw in IBM Langflow OSS allows an authenticated user to escalate from limited flow-building privileges to full arbitrary command execution on the server. By crafting a malicious 'type' field in a saved flow and triggering a build via a wrapper flow, an attacker bypasses the LANGFLOW_ALLOW_CUSTOM_COMPONENTS=false safeguard intended to block custom code execution. This effectively hands the attacker OS-level control of the agent server process.
Technical Analysis
Langflow flows reference component 'type' values that are resolved and instantiated by the server during a build operation. The vulnerability allows an attacker to inject a crafted type value into a saved flow definition; when a separate 'wrapper' flow references and builds this component, the server resolves and executes it without properly enforcing the custom-components policy flag. This crosses the trust boundary between the low-privilege 'flow author' role and the server process itself, since flow definitions—normally treated as configuration data—are deserialized into executable code paths. The entry point is any authenticated Langflow user with flow save/build permissions, and the impact is full compromise of the server process, including access to any credentials, tool integrations, or downstream agents/MCP servers reachable from that host.
Affected Systems
Langflow
Detection Signatures
- Flow JSON/YAML definitions containing unexpected or non-standard 'type' field values referencing internal/system classes
- Build requests for flows that reference components not present in the standard component registry
- Server logs showing subprocess/os-level command execution originating from flow build/import endpoints
- Unexpected child processes spawned by the langflow server process during flow build operations
- LANGFLOW_ALLOW_CUSTOM_COMPONENTS=false configured but custom component build activity still observed in logs
Remediation Steps
- 1
Patch Langflow
Upgrade to the fixed Langflow release that addresses CVE-2026-19295 as soon as it is available from IBM/Langflow maintainers.
- 2
Restrict flow authoring permissions
Limit which authenticated users can save or build flows; treat flow-save privileges as equivalent to code-execution privileges until patched.
- 3
Validate flow 'type' fields server-side
Implement strict allow-listing and schema validation on component type resolution during flow save and build, independent of the custom-components flag.
- 4
Isolate build execution
Run flow build/execution in a sandboxed or containerized environment with least-privilege OS permissions, network egress restrictions, and no access to sensitive secrets.
- 5
Audit and monitor
Review logs for anomalous flow builds referencing unusual types, and monitor server process activity for unexpected command execution.
CVE / Advisory IDs
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