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Streamable HTTP mode exposes LINE Desktop read/send tools without MCP authentication

High severity GitHub Reviewed Published May 25, 2026 in dtwang/line-desktop-mcp • Updated Jun 26, 2026

Package

npm line-desktop-mcp (npm)

Affected versions

<= 1.1.1

Patched versions

1.1.2

Description

Streamable HTTP mode exposes LINE Desktop read/send tools without MCP authentication

Summary

line-desktop-mcp supports a --http-mode Streamable HTTP transport for use with clients such as n8n. In this mode the server binds to 0.0.0.0 and exposes the MCP /mcp endpoint without an MCP-layer authentication check. Any network client that can reach the port can initialize a session, list tools, and call tools that read LINE Desktop chat history or send LINE messages through the already logged-in desktop application.

This is High for deployments where the HTTP port is reachable beyond the local host, because the server acts with the user authority of the logged-in LINE Desktop session. It is lower if the listener is strictly firewalled to trusted local clients.

Affected version

Repository: dtwang/line-desktop-mcp

Current source checked: fbed0d2d3048e63f48a356a1267ed8ec5e78f3ae on main, committed 2026-05-14.

Published npm package checked: line-desktop-mcp@1.1.1.

Source evidence

README.md documents Streamable HTTP mode:

npx line-desktop-mcp@latest --http-mode --port 3000

The same README documents MCP endpoints at /mcp and explains that this mode is intended for clients such as n8n.

src/server.js registers LINE Desktop tools including:

  • get_line_chatroom_history_default
  • get_line_chatroom_history_long
  • get_line_chatroom_history_short
  • send_message_manual
  • send_message_auto

Those tool handlers call into the desktop automation layer: getChatHistory(...) and sendChatMessage(...).

In HTTP mode, src/server.js creates an Express app and Streamable HTTP transport, accepts POSTs to /mcp, creates sessions, connects the transport to the MCP server, and calls transport.handleRequest(...). I did not find an authentication or bearer-token check before session creation or tool invocation.

The listener is explicitly network-bound:

app.listen(port, 0.0.0.0, () => {
  console.error(`LINE Desktop MCP Server running on Streamable HTTP mode`);
  console.error(`  Local:   http://127.0.0.1:${port}${endpoint}`);
  console.error(`  Network: http://0.0.0.0:${port}${endpoint}`);
});

Vulnerability chain

  1. A user starts the server with --http-mode --port 3000.
  2. The server binds on 0.0.0.0:3000, not only loopback.
  3. A network client reaches /mcp and sends the normal MCP initialize request.
  4. The server creates a Streamable HTTP session without authenticating the caller.
  5. The caller can list and invoke LINE Desktop tools.
  6. Tool calls execute through the logged-in LINE Desktop application on the user workstation.

Impact

An unauthenticated network client can read LINE chat history through the MCP history tools and can send LINE messages through the send-message tools, including send_message_auto when the tool call requests immediate sending. The attacker does not need LINE credentials or a LINE API token; they only need network reachability to the MCP HTTP port.

The practical impact is disclosure of private LINE conversations and unauthorized messages sent as the logged-in desktop user.

Suggested fix

Require authentication before accepting Streamable HTTP MCP sessions or tool calls. For example:

  • require a bearer token or local secret when --http-mode is used;
  • bind HTTP mode to 127.0.0.1 by default unless the operator explicitly opts into network exposure;
  • refuse to start 0.0.0.0 HTTP mode without authentication;
  • document that host.docker.internal / n8n setups must still authenticate to the MCP server.

A defense-in-depth improvement would also keep send_message_auto disabled unless explicitly enabled by a server-side flag, because it converts MCP tool access into immediate message sending as the desktop user.

References

@dtwang dtwang published to dtwang/line-desktop-mcp May 25, 2026
Published by the National Vulnerability Database Jun 19, 2026
Published to the GitHub Advisory Database Jun 26, 2026
Reviewed Jun 26, 2026
Last updated Jun 26, 2026

Severity

High

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v4 base metrics

Exploitability Metrics
Attack Vector Network
Attack Complexity Low
Attack Requirements None
Privileges Required None
User interaction None
Vulnerable System Impact Metrics
Confidentiality High
Integrity Low
Availability None
Subsequent System Impact Metrics
Confidentiality None
Integrity None
Availability None

CVSS v4 base metrics

Exploitability Metrics
Attack Vector: This metric reflects the context by which vulnerability exploitation is possible. This metric value (and consequently the resulting severity) will be larger the more remote (logically, and physically) an attacker can be in order to exploit the vulnerable system. The assumption is that the number of potential attackers for a vulnerability that could be exploited from across a network is larger than the number of potential attackers that could exploit a vulnerability requiring physical access to a device, and therefore warrants a greater severity.
Attack Complexity: This metric captures measurable actions that must be taken by the attacker to actively evade or circumvent existing built-in security-enhancing conditions in order to obtain a working exploit. These are conditions whose primary purpose is to increase security and/or increase exploit engineering complexity. A vulnerability exploitable without a target-specific variable has a lower complexity than a vulnerability that would require non-trivial customization. This metric is meant to capture security mechanisms utilized by the vulnerable system.
Attack Requirements: This metric captures the prerequisite deployment and execution conditions or variables of the vulnerable system that enable the attack. These differ from security-enhancing techniques/technologies (ref Attack Complexity) as the primary purpose of these conditions is not to explicitly mitigate attacks, but rather, emerge naturally as a consequence of the deployment and execution of the vulnerable system.
Privileges Required: This metric describes the level of privileges an attacker must possess prior to successfully exploiting the vulnerability. The method by which the attacker obtains privileged credentials prior to the attack (e.g., free trial accounts), is outside the scope of this metric. Generally, self-service provisioned accounts do not constitute a privilege requirement if the attacker can grant themselves privileges as part of the attack.
User interaction: This metric captures the requirement for a human user, other than the attacker, to participate in the successful compromise of the vulnerable system. This metric determines whether the vulnerability can be exploited solely at the will of the attacker, or whether a separate user (or user-initiated process) must participate in some manner.
Vulnerable System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the VULNERABLE SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the VULNERABLE SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the VULNERABLE SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
Subsequent System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the SUBSEQUENT SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the SUBSEQUENT SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the SUBSEQUENT SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:L/VA:N/SC:N/SI:N/SA:N

EPSS score

Exploit Prediction Scoring System (EPSS)

This score estimates the probability of this vulnerability being exploited within the next 30 days. Data provided by FIRST.
(24th percentile)

Weaknesses

Missing Authentication for Critical Function

The product does not perform any authentication for functionality that requires a provable user identity or consumes a significant amount of resources. Learn more on MITRE.

Missing Authorization

The product does not perform an authorization check when an actor attempts to access a resource or perform an action. Learn more on MITRE.

CVE ID

CVE-2026-49357

GHSA ID

GHSA-4hf8-5mjm-rfgq

Source code

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