GHSA-qq9g-96v4-m3cj

## Summary

The Select schema plugin in `@pdfme/schemas` constructs HTML from template-defined option values using unsanitized string interpolation and sets it via `innerHTML`, enabling arbitrary JavaScript execution.

## Details

In `packages/schemas/src/select/index.ts`, lines 159-164, the Select schema's `ui` renderer builds `<option>` elements by directly interpolating option values from the template into an HTML string:

```typescript const options = Array.isArray(schema.options) ? schema.options : []; selectElement.innerHTML = options .map( (option) => `<option value="${option}" ${option === value ? 'selected' : ''}>${option}</option>`, ) .join(''); ```

The `option` values come from `schema.options`, which is an array of strings defined in the template JSON. These values are interpolated directly into the HTML string without any escaping of `<`, `>`, `"`, `&`, or other HTML-special characters. An option value containing `">` breaks out of the `value` attribute and allows injection of arbitrary HTML elements and event handlers.

## Proof of Concept

Loading the following template into a pdfme Form or Designer component triggers JavaScript execution:

```json { "basePdf": { "width": 210, "height": 297, "padding": [20, 20, 20, 20] }, "schemas": [[ { "name": "malicious_select", "type": "select", "content": "Normal", "options": [ "Normal", "\"></option><img src=x onerror=\"alert(document.domain)\">" ], "position": { "x": 20, "y": 20 }, "width": 80, "height": 10 } ]] } ```

The injected `<img onerror>` element executes JavaScript because it is parsed as HTML when assigned to `selectElement.innerHTML`.

## Attack Vectors

The `options` array is defined in the template (not by form-filling end users). The attack requires a malicious template to be loaded, which can happen via: 1. File upload (e.g., "Load Template" functionality in applications) 2. Shared/imported templates in multi-tenant applications 3. Templates stored in databases without content sanitization 4. The `updateTemplate()` API being called with untrusted data

This vulnerability is triggered in Form mode (for non-readOnly select fields) and Designer mode when the select element is rendered.

## Impact

An attacker who can supply a malicious template can execute arbitrary JavaScript in the browser of any user who views or interacts with the template. This enables: - Session hijacking via cookie/token theft - Keylogging of form input data - Phishing and page modification - Data exfiltration

## Suggested Fix

Use DOM APIs to create option elements safely instead of string interpolation:

```typescript options.forEach((option) => { const optionEl = document.createElement('option'); optionEl.value = option; optionEl.textContent = option; if (option === value) optionEl.selected = true; selectElement.appendChild(optionEl); }); ```

Alternatively, HTML-encode option values before interpolation: ```typescript const escape = (s) => s.replace(/&/g, '&amp;').replace(/"/g, '&quot;').replace(/</g, '&lt;').replace(/>/g, '&gt;'); ```