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fix: Use a null prototype object for this.files #766

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Merged
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Jun 29, 2021
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fix: Use a null prototype object for this.files #766

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fix: Use a null prototype object for this.files
MichaelAquilina Jun 14, 2021
d024c22
test: Add test case for loading zip filenames which shadow method names
MichaelAquilina Jun 14, 2021
bb38812
Ensure prototype isn't modified by zip file
Stuk Jun 23, 2021
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5 changes: 4 additions & 1 deletion lib/index.js
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Expand Up @@ -19,7 +19,10 @@ function JSZip() {
// "folder/" : {...},
// "folder/data.txt" : {...}
// }
this.files = {};
// NOTE: we use a null prototype because we do not
// want filenames like "toString" coming from a zip file
// to overwrite methods and attributes in a normal Object.
this.files = Object.create(null);

this.comment = null;

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6 changes: 3 additions & 3 deletions lib/object.js
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Expand Up @@ -179,16 +179,16 @@ var out = {
*/
forEach: function(cb) {
var filename, relativePath, file;
/* jshint ignore:start */
// ignore warning about unwanted properties because this.files is a null prototype object
for (filename in this.files) {
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@MichaelAquilina MichaelAquilina Jun 14, 2021

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@Stuk we could use for(filename of Object.keys(this.files)) { here instead, but it seems jszip is targetting es3 in jshintrc.

We could set this to es6 but I assume this would break for a number of users and you would want to avoid that?

This is the error that comes up if I change it:

   ./lib/object.js
    182 |        for (filename of Object.keys(this.files)) {
                               ^ 'for of' is available in ES6 (use 'esversion: 6') or Mozilla JS extensions (use moz).

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@Stuk Stuk Jun 14, 2021

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Yeah, there's a bigger task for upgrading the tooling and browser compatibility for this library. The approach here looks good.

if (!this.files.hasOwnProperty(filename)) {
continue;
}
file = this.files[filename];
relativePath = filename.slice(this.root.length, filename.length);
if (relativePath && filename.slice(0, this.root.length) === this.root) { // the file is in the current root
cb(relativePath, file); // TODO reverse the parameters ? need to be clean AND consistent with the filter search fn...
}
}
/* jshint ignore:end */
},

/**
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13 changes: 13 additions & 0 deletions test/asserts/load.js
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Expand Up @@ -17,6 +17,19 @@ QUnit.module("load", function () {
})['catch'](JSZipTestUtils.assertNoError);
});

JSZipTestUtils.testZipFile("Load files which shadow Object prototype methods", "ref/pollution.zip", function(assert, file) {
var done = assert.async();
assert.ok(typeof file === "string");
JSZip.loadAsync(file)
.then(function (zip) {
assert.notEqual(Object.getPrototypeOf(zip.files), zip.files.__proto__);
return zip.file("__proto__").async("string"); })
.then(function(result) {
assert.equal(result, "hello\n", "the zip was correctly read.");
done();
})['catch'](JSZipTestUtils.assertNoError);
});
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@Stuk Stuk Jun 15, 2021

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I tried removing the Object.create(null) fix, to see if this test failed and it didn't, so I don't think this is actually catching the issue?

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@MichaelAquilina MichaelAquilina Jun 16, 2021

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That's a good point - but I'm not entirely sure how to test this change because essentially this change is about making sure toString / __proto__ / __constructor__ etc are not available in the first place.

I guess I could add a test that shows that toString raises an error - but I'm not sure how useful that would be in the long run?

The reasoning for this test specifically was to show that files with names that shadow standard Object method names can still be accessed correctly


JSZipTestUtils.testZipFile("load(string) handles bytes > 255", "ref/all.zip", function(assert, file) {
var done = assert.async();
// the method used to load zip with ajax will remove the extra bits.
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