Low

Prototype pollution in emit function

Disclosed: 17.04.2024
Updated: 11.10.2026 10:22

Summary

A prototype pollution in derby can crash the application, if the application author has atypical HTML templates that feed user input into an object key.

Attribute keys are almost always developer-controlled, not end-user-controlled, so this shouldn't be an issue in practice for most applications.

Details

emit(context: Context, target: T) {
  const node = traverseAndCreate(context.controller, this.segments);
    node[this.lastSegment] = target;
    this.addListeners(target, node, this.lastSegment);
}

The emit() function in src/templates/templates.ts is called without sanitizing the variable this.lastSegment . The variable this.lastSegment can be set to __proto__, and this will pollute the prototype of Javascipt Object (node['__proto__'] = target).

PoC

To reproduce this vulnerability, you can adjust the test case ignores DOM mutations in components\' create() in test/dom/ComponentHarness.mocha.js.

it('ignores DOM mutations in components\' create()', function() {
      function Box() {}
      Box.view = {
        is: 'box',
-        source: '<index:><div class="box" as="boxElement"></div>'
+        source: '<index:><div class="box" as="__proto__"></div>'
      };
      Box.prototype.create = function() {
        this.boxElement.className = 'box-changed-in-create';
      };
      var harness = runner.createHarness('<view is="box" />', Box);
      expect(harness).to.render('<div class="box"></div>');
});

When as attribute is controlled by attackers, the variable in this.lastSegment will exactly take value __proto__ and prototype pollution happens.

Patch

Add a check on this.lastSegment can prevent this attack.

emit(context: Context, target: T) {
  const node = traverseAndCreate(context.controller, this.segments);
+  if (this.lastSegment.includes('__proto__') || this.lastSegment.includes('prototype')) {
+    throw new Error('Unsafe code detected');
+  }
    node[this.lastSegment] = target;
    this.addListeners(target, node, this.lastSegment);
}

Affected software

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Platform	Package	Vulnerable versions	Fixed in
npm package	derby	< 2.3.2, >= 3.0.0, < 3.0.2, >= 4.0.0-beta1, < 4.0.0-beta.11	2.3.2, 3.0.2, 4.0.0-beta.11

References

CVSS score -

Weakness (CWE): CWE-1321
Platform: npm
Package: derby
Disclosed: 17.04.2024
Updated: 11.10.2026 10:22

Sources and licenses

OSV / GitHub Advisory Database - GHSA-82jv-9wjw-pqh6 - CC BY 4.0

Vulnerability history: derby

All published vulnerabilities of this package (npm package), newest first. Shows whether this is a one-off slip or a package that needs watching.

This is the only known vulnerability of this package.

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