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child_process: harden against prototype pollution #48726

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Jul 14, 2023
Merged

child_process: harden against prototype pollution #48726

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7 changes: 5 additions & 2 deletions lib/child_process.js
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Original file line number Diff line number Diff line change
Expand Up @@ -136,7 +136,7 @@ function fork(modulePath, args = [], options) {
if (options != null) {
validateObject(options, 'options');
}
options = { ...options, shell: false };
options = { __proto__: null, ...options, shell: false };
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Not related to this PR, but I wonder if we should use { __proto__: options, shell: false } and let users decide if they want prototype pollution or not.

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Wouldn't it make this object affected by subsequent mutations outside?
In fact, I wonder if we should use structuredClone() or at least make copies of object properties like .env to avoid race conditions if multiple fork()s are called with reused options.

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Wouldn't it make this object affected by subsequent mutations outside?

I guess it depends if we read the properties in the same tick or not (which I expect we do most of the time, but I haven't checked).

In fact, I wonder if we should use structuredClone()

That wouldn't help with inconsistency of our API: sometimes, we dismiss inherited properties, sometimes we don't. But it's clearly not a big deal as I don't think we ever received any bug report regarding that.

or at least make copies of object properties like .env to avoid race conditions if multiple fork()s are called with reused options.

but wouldn't folks expect the same env to be shared if they supply the same object? The fact that no one complains makes me think we're overthinking it 😅

options.execPath = options.execPath || process.execPath;
validateArgumentNullCheck(options.execPath, 'options.execPath');

Expand Down Expand Up @@ -194,7 +194,7 @@ function normalizeExecArgs(command, options, callback) {
}

// Make a shallow copy so we don't clobber the user's options object.
options = { ...options };
options = { __proto__: null, ...options };
options.shell = typeof options.shell === 'string' ? options.shell : true;

return {
Expand Down Expand Up @@ -327,6 +327,7 @@ function execFile(file, args, options, callback) {
({ file, args, options, callback } = normalizeExecFileArgs(file, args, options, callback));

options = {
__proto__: null,
encoding: 'utf8',
timeout: 0,
maxBuffer: MAX_BUFFER,
Expand Down Expand Up @@ -701,6 +702,7 @@ function normalizeSpawnArguments(file, args, options) {

return {
// Make a shallow copy so we don't clobber the user's options object.
__proto__: null,
...options,
args,
cwd,
Expand Down Expand Up @@ -826,6 +828,7 @@ function spawn(file, args, options) {
*/
function spawnSync(file, args, options) {
options = {
__proto__: null,
maxBuffer: MAX_BUFFER,
...normalizeSpawnArguments(file, args, options),
};
Expand Down
59 changes: 59 additions & 0 deletions test/parallel/test-child-process-prototype-tampering.mjs
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Original file line number Diff line number Diff line change
@@ -0,0 +1,59 @@
import * as common from '../common/index.mjs';
import * as fixtures from '../common/fixtures.mjs';
import { EOL } from 'node:os';
import { strictEqual } from 'node:assert';
import cp from 'node:child_process';

// TODO(LiviaMedeiros): test on different platforms
if (!common.isLinux)
common.skip();

const expectedCWD = process.cwd();
const expectedUID = process.getuid();

for (const tamperedCwd of ['', '/tmp', '/not/existing/malicious/path', 42n]) {
Object.prototype.cwd = tamperedCwd;

cp.exec('pwd', common.mustSucceed((out) => {
strictEqual(`${out}`, `${expectedCWD}${EOL}`);
}));
strictEqual(`${cp.execSync('pwd')}`, `${expectedCWD}${EOL}`);
cp.execFile('pwd', common.mustSucceed((out) => {
strictEqual(`${out}`, `${expectedCWD}${EOL}`);
}));
strictEqual(`${cp.execFileSync('pwd')}`, `${expectedCWD}${EOL}`);
cp.spawn('pwd').stdout.on('data', common.mustCall((out) => {
strictEqual(`${out}`, `${expectedCWD}${EOL}`);
}));
strictEqual(`${cp.spawnSync('pwd').stdout}`, `${expectedCWD}${EOL}`);

delete Object.prototype.cwd;
}

for (const tamperedUID of [0, 1, 999, 1000, 0n, 'gwak']) {
Object.prototype.uid = tamperedUID;

cp.exec('id -u', common.mustSucceed((out) => {
strictEqual(`${out}`, `${expectedUID}${EOL}`);
}));
strictEqual(`${cp.execSync('id -u')}`, `${expectedUID}${EOL}`);
cp.execFile('id', ['-u'], common.mustSucceed((out) => {
strictEqual(`${out}`, `${expectedUID}${EOL}`);
}));
strictEqual(`${cp.execFileSync('id', ['-u'])}`, `${expectedUID}${EOL}`);
cp.spawn('id', ['-u']).stdout.on('data', common.mustCall((out) => {
strictEqual(`${out}`, `${expectedUID}${EOL}`);
}));
strictEqual(`${cp.spawnSync('id', ['-u']).stdout}`, `${expectedUID}${EOL}`);

delete Object.prototype.uid;
}

{
Object.prototype.execPath = '/not/existing/malicious/path';

// Does not throw ENOENT
cp.fork(fixtures.path('empty.js'));

delete Object.prototype.execPath;
}