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reject prototype-polluting path segments in Path.set #5756

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reject prototype-polluting path segments in Path.set #5756

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9 changes: 9 additions & 0 deletions lib/utils/path.js
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Original file line number Diff line number Diff line change
Expand Up @@ -218,6 +218,15 @@ export function set(root, path, value) {
let prop = root;
let parts = split(path);
let last = parts[parts.length-1];
// Refuse to traverse or write through keys that resolve to the prototype
// chain, otherwise a path such as `__proto__.x` or `constructor.prototype.x`
// mutates `Object.prototype` instead of `root`.
for (let i=0; i<parts.length; i++) {
if (parts[i] === '__proto__' || parts[i] === 'prototype' ||
parts[i] === 'constructor') {
return;
}
}
if (parts.length > 1) {
// Loop over path parts[0..n-2] and dereference
for (let i=0; i<parts.length-1; i++) {
Expand Down
14 changes: 13 additions & 1 deletion test/unit/path.html
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Expand Up @@ -18,7 +18,7 @@
<body>

<script type="module">
import { isAncestor, isDeep, isDescendant, root, matches, translate } from '../../lib/utils/path.js';
import { isAncestor, isDeep, isDescendant, root, matches, translate, set } from '../../lib/utils/path.js';
suite('path utilities', function() {

test('root()', function() {
Expand Down Expand Up @@ -77,5 +77,17 @@
assert.equal(matches('foo.bar','foo.baz'), false);
assert.equal(matches('foo.bar','foo.bars'), false);
});

test('set() does not pollute the prototype', function() {
assert.equal(set({}, '__proto__.polluted', true), undefined);
assert.equal(set({}, 'constructor.prototype.polluted', true), undefined);
assert.equal({}.polluted, undefined);

const obj = {a: {b: 1}};
assert.equal(set(obj, 'a.b', 2), 'a.b');
assert.equal(obj.a.b, 2);
assert.equal(set(obj, 'a', 3), 'a');
assert.equal(obj.a, 3);
});
});
</script>