LangBot MCP Server Configuration Authorization Bypass Leading to Remote Code Execution
First seen Aug 20, 2026 · Updated Aug 20, 2026 · CVSS 8.8
LangBot, an LLM-based IM bot platform, allows any authenticated user to configure a STDIO MCP server, which the backend uses to launch an arbitrary subprocess with server-level privileges. This means a low-privileged account holder can achieve full remote code execution on the LangBot host, leading to data disclosure, tampering, and service disruption. No fix is currently available, making this a high-priority, actively exploitable weakness.
Technical Analysis
The vulnerability resides in src/langbot/pkg/provider/tools/loaders/mcp.py, where StdioServerParameters directly accepts user-supplied command and argument values from the Extensions MCP configuration UI/API without verifying that the requesting user has sufficient privilege to define server-side executable commands. Because MCP STDIO servers are launched as local subprocesses under the LangBot service account, any authenticated user (including self-registered accounts) can set the command field to an attacker-controlled binary or shell command, resulting in arbitrary code execution with the service's privileges. This crosses a critical trust boundary: MCP tool configuration is intended to be an administrative capability, but here it is exposed at the standard authenticated-user layer, effectively turning the tool-loading mechanism into an unauthenticated-to-privileged command execution primitive. The attacker gains full compromise of the LangBot server process, potentially pivoting to connected systems, stored credentials, and other integrated LLM/agent tooling.
Affected Systems
LangBot; protocols: MCP
Detection Signatures
- Unexpected new entries in Extensions/MCP server configuration created by non-admin accounts
- STDIO MCP server 'command' field pointing to shell interpreters (sh, bash, cmd.exe, powershell) or unusual binaries
- Subprocess spawn events from the LangBot service process correlating with MCP config changes
- New or modified MCP server configs with arguments containing pipes, redirects, or encoded payloads
- Authenticated API calls to MCP configuration endpoints from newly created or low-privilege user accounts
Remediation Steps
- 1
Restrict MCP configuration to administrators
Enforce role-based access control so only trusted/admin accounts can create or modify STDIO MCP server configurations, not any authenticated user.
- 2
Sandbox or disable STDIO MCP execution
Run MCP STDIO subprocesses in a restricted, low-privilege sandbox (container, seccomp, minimal service account) separate from the main LangBot service, or disable STDIO server support until a patch is released.
- 3
Validate and allowlist commands
Implement strict allowlisting of permitted executables/arguments for MCP server commands and reject arbitrary shell invocations.
- 4
Monitor and audit configuration changes
Add audit logging and alerting for any changes to Extensions/MCP configurations, especially from non-admin accounts, and review existing configs for tampering.
- 5
Apply vendor patch when available
Track the LangBot repository/advisory for a fix and upgrade promptly once a patched version addressing this authorization gap is released.
CVE / Advisory IDs
Industries Most Exposed
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