Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

disallow accessing Function constructor #27

Merged
merged 4 commits into from Nov 19, 2019
Merged
Show file tree
Hide file tree
Changes from all commits
Commits
File filter

Filter by extension

Filter by extension

Conversations
Failed to load comments.
Jump to
Jump to file
Failed to load files.
Diff view
Diff view
10 changes: 8 additions & 2 deletions index.js
Expand Up @@ -101,11 +101,13 @@ module.exports = function (ast, vars) {
if((obj === FAIL) || (typeof obj == 'function')){
return FAIL;
}
if (node.property.type === 'Identifier') {
if (node.property.type === 'Identifier' && !node.computed) {
if (isUnsafeProperty(node.property.name)) return FAIL;
return obj[node.property.name];
}
var prop = walk(node.property);
if (prop === FAIL) return FAIL;
if (prop === null || prop === FAIL) return FAIL;
if (isUnsafeProperty(prop)) return FAIL;
return obj[prop];
}
else if (node.type === 'ConditionalExpression') {
Expand Down Expand Up @@ -176,3 +178,7 @@ module.exports = function (ast, vars) {

return result === FAIL ? undefined : result;
};

function isUnsafeProperty(name) {
return name === 'constructor' || name === '__proto__';
}
43 changes: 42 additions & 1 deletion test/eval.js
Expand Up @@ -79,4 +79,45 @@ test('MemberExpressions from Functions unresolved', function(t) {
var ast = parse(src).body[0].expression;
var res = evaluate(ast, {});
t.equal(res, undefined);
});
});

test('disallow accessing constructor or __proto__', function (t) {
t.plan(4)

var someValue = {};

var src = 'object.constructor';
var ast = parse(src).body[0].expression;
var res = evaluate(ast, { vars: { object: someValue } });
t.equal(res, undefined);

var src = 'object["constructor"]';
var ast = parse(src).body[0].expression;
var res = evaluate(ast, { vars: { object: someValue } });
t.equal(res, undefined);

var src = 'object.__proto__';
var ast = parse(src).body[0].expression;
var res = evaluate(ast, { vars: { object: someValue } });
t.equal(res, undefined);

var src = 'object["__pro"+"t\x6f__"]';
var ast = parse(src).body[0].expression;
var res = evaluate(ast, { vars: { object: someValue } });
t.equal(res, undefined);
});


test('constructor at runtime only', function(t) {
t.plan(2)

var src = '(function myTag(y){return ""[!y?"__proto__":"constructor"][y]})("constructor")("console.log(process.env)")()'
var ast = parse(src).body[0].expression;
var res = evaluate(ast);
t.equal(res, undefined);

var src = '(function(prop) { return {}[prop ? "benign" : "constructor"][prop] })("constructor")("alert(1)")()'
var ast = parse(src).body[0].expression;
var res = evaluate(ast);
t.equal(res, undefined);
});