CVE-2026-19244 Overview
CVE-2026-19244 is an improper access control vulnerability [CWE-266] in HKUDS nanobot versions up to and including 0.2.1. The flaw exists in the connect_mcp_servers function within nanobot/agent/tools/mcp.py, part of the Model Context Protocol (MCP) enabledTools Scope Handler component. MCP resource and prompt wrappers could be registered outside the intended enabledTools scope, breaking the registration boundary. An attacker with high privileges can exploit this remotely over the network. The exploit is public. Upgrading to version 0.3.0 remediates the issue via patch 4436.
Critical Impact
Remote authenticated attackers can access MCP resources and prompts outside the intended enabledTools scope, resulting in limited confidentiality, integrity, and availability impact.
Affected Products
- HKUDS nanobot versions up to 0.2.1
- Component: MCP enabledTools Scope Handler
- File: nanobot/agent/tools/mcp.py
Discovery Timeline
- 2026-08-07 - CVE-2026-19244 published to NVD
- 2026-08-12 - Last updated in NVD database
Technical Details for CVE-2026-19244
Vulnerability Analysis
The vulnerability resides in the connect_mcp_servers function of nanobot/agent/tools/mcp.py. This function handles registration of MCP capabilities exposed to the agent. According to the maintainer, both reported issues share the same root cause: MCP resource and prompt wrappers could be registered outside the intended enabledTools scope. The registration boundary did not correctly enforce the configured scope, so wrappers not meant to be enabled were still made available.
Exploitation requires network access and authenticated high-privilege access. Successful exploitation grants access to MCP resources and prompts that should have been out of scope. Public exploit code is available, referenced in a GitHub Gist linked from the VulDB entry.
Root Cause
The root cause is an improper enforcement of the enabledTools scope during MCP server connection. Resource and prompt wrappers were registered without validating whether they fell within the operator-defined scope. This is classified under [CWE-266: Incorrect Privilege Assignment], where components receive privileges or exposure beyond what the configuration intends.
Attack Vector
The attack vector is network-based and requires high privileges with no user interaction. An authenticated attacker interacting with the nanobot MCP interface can invoke resources or prompts that the operator explicitly excluded from enabledTools. Because the boundary is enforced at registration time, out-of-scope wrappers become reachable through normal MCP client calls once the server is running. See the Nanobot Issue #4435 and Pull Request #4436 for technical context.
No verified exploitation code is reproduced here. Refer to the public gist referenced in the advisory for demonstration material.
Detection Methods for CVE-2026-19244
Indicators of Compromise
- MCP client invocations targeting resource or prompt names not present in the deployed enabledTools configuration.
- Unexpected entries in nanobot agent logs referencing wrappers registered by connect_mcp_servers outside the declared scope.
- Nanobot processes running versions 0.2.1 or earlier still reachable on the network.
Detection Strategies
- Inventory all nanobot deployments and compare installed versions against 0.3.0. Any version at or below 0.2.1 is affected.
- Audit MCP server configurations and compare the runtime-registered tools, resources, and prompts against the enabledTools allowlist to identify scope violations.
- Review authentication logs for high-privilege sessions issuing MCP calls that do not match documented workflows.
Monitoring Recommendations
- Enable verbose logging on the nanobot agent to capture MCP registration events and client requests, then forward these to a centralized log store.
- Alert on any MCP resource or prompt access referencing names outside the approved enabledTools list.
- Track outbound requests from nanobot to MCP servers to detect connections to unexpected endpoints.
How to Mitigate CVE-2026-19244
Immediate Actions Required
- Upgrade HKUDS nanobot to version 0.3.0 or later, which includes patch 4436 correcting the registration boundary.
- Restrict network reachability of nanobot MCP endpoints to trusted management networks only until patching is complete.
- Rotate credentials for any high-privilege accounts that could authenticate to a vulnerable nanobot instance.
Patch Information
The fix is delivered in nanobot release v0.3.0 via Pull Request #4436. The patch corrects the registration logic in connect_mcp_servers so that MCP resource and prompt wrappers honor the enabledTools scope. Maintainers confirmed both submitted reports were addressed by the same fix.
Workarounds
- If immediate upgrade is not possible, remove or disable MCP servers whose resources or prompts must remain out of scope.
- Limit access to the nanobot control interface to a minimal set of administrators, reducing the population able to satisfy the high-privilege precondition.
- Deploy network-layer access controls to block untrusted clients from reaching the nanobot MCP listener.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
