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Fixed controlFlowFlattening breaking short-circuit evaluation of &&, || and ?? #1459

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Merged
sanex3339 merged 1 commit into from
Sep 30, 2026
Merged

Fixed controlFlowFlattening breaking short-circuit evaluation of &&, || and ?? #1459

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1 change: 1 addition & 0 deletions CHANGELOG.md
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Expand Up @@ -3,6 +3,7 @@ Change Log
v5.8.1
---
* Fixed `transformObjectKeys` making default parameter objects shared across calls. Fixed https://github.com/javascript-obfuscator/javascript-obfuscator/issues/1455
* Fixed `controlFlowFlattening` breaking short-circuit evaluation of `&&`, `||` and `??`. Fixed https://github.com/javascript-obfuscator/javascript-obfuscator/issues/1456

v5.8.0
---
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21 changes: 20 additions & 1 deletion .../control-flow-transformers/control-flow-replacers/LogicalExpressionControlFlowReplacer.ts
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Expand Up @@ -90,7 +90,10 @@ export class LogicalExpressionControlFlowReplacer extends ExpressionWithOperator
leftExpression: ESTree.Expression,
rightExpression: ESTree.Expression
): boolean {
if (this.expressionContainsProhibitedNodes(rightExpression)) {
if (
this.expressionContainsProhibitedNodes(rightExpression) ||
!this.isSafeToEvaluateEagerly(rightExpression)
) {
return true;
}

Expand All @@ -112,6 +115,22 @@ export class LogicalExpressionControlFlowReplacer extends ExpressionWithOperator
});
}

/**
* The right operand becomes an argument of the control flow storage call and is always evaluated,
* so short-circuit evaluation is lost. Only literals are safe to evaluate eagerly: identifiers may throw
* (temporal dead zone, undeclared globals) and object expressions may throw or have side effects
*
* @param {Expression} expression
* @returns {boolean}
*/
private isSafeToEvaluateEagerly(expression: ESTree.Expression): boolean {
const nodeForCheck: ESTree.Node = NodeGuards.isUnaryExpressionNode(expression)
? NodeUtils.getUnaryExpressionArgumentNode(expression)
: expression;

return NodeGuards.isLiteralNode(nodeForCheck);
}

/**
* @param {Expression} expression
* @returns {boolean}
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60 changes: 60 additions & 0 deletions test/functional-tests/issues/issue1456.spec.ts
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@@ -0,0 +1,60 @@
import { assert } from 'chai';

import { NO_ADDITIONAL_NODES_PRESET } from '../../../src/options/presets/NoCustomNodes';

import { JavaScriptObfuscator } from '../../../src/JavaScriptObfuscatorFacade';

//
// https://github.com/javascript-obfuscator/javascript-obfuscator/issues/1456
//
describe('Issue #1456', () => {
describe('`controlFlowFlattening` should keep short-circuit evaluation of logical expressions', () => {
const samples: { name: string; code: string; expectedResult: unknown }[] = [
{
name: 'Variant #1: `&&` with object expression that reads property of falsy left operand',
code: 'function size(img) { return img && { width: img.width }; } return size(null);',
expectedResult: null
},
{
name: 'Variant #2: `&&` with identifier in temporal dead zone',
code: 'function pick(ready) { return ready && late; } var result = pick(false); let late = 1; return result;',
expectedResult: false
},
{
name: 'Variant #3: `&&` with undeclared global identifier',
code: 'function pick(ready) { return ready && undeclaredGlobal1456; } return pick(false);',
expectedResult: false
},
{
name: 'Variant #4: `||` with side effect inside object expression',
code: 'var count = 0; function next(seen) { return seen || { n: ++count }; } next(true); return count;',
expectedResult: 0
},
{
name: 'Variant #5: `??` with unary expression over identifier in temporal dead zone',
code: 'function pick(value) { return value ?? !late; } var result = pick(1); let late = 1; return result;',
expectedResult: 1
}
];

samples.forEach(({ name, code, expectedResult }) => {
describe(name, () => {
let result: unknown;

before(() => {
const obfuscatedCode: string = JavaScriptObfuscator.obfuscate(code, {
...NO_ADDITIONAL_NODES_PRESET,
controlFlowFlattening: true,
controlFlowFlatteningThreshold: 1
}).getObfuscatedCode();

result = new Function(obfuscatedCode)();
});

it('should not evaluate the skipped right operand', () => {
assert.strictEqual(result, expectedResult);
});
});
});
});
});
48 changes: 47 additions & 1 deletion ...ers/logical-expression-control-flow-replacer/LogicalExpressionControlFlowReplacer.spec.ts
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Expand Up @@ -99,7 +99,7 @@ describe('LogicalExpressionControlFlowReplacer', function () {

describe('Variant #3 - single logical expression with unary expression', () => {
const controlFlowStorageCallRegExp: RegExp = new RegExp(
`var ${variableMatch} *= *${variableMatch}\\['\\w{5}'\\]\\(!${variableMatch}, *!${variableMatch}\\);`
`var ${variableMatch} *= *${variableMatch}\\['\\w{5}'\\]\\(!${variableMatch}, *!!\\[\\]\\);`
);

let obfuscatedCode: string;
Expand Down Expand Up @@ -140,5 +140,51 @@ describe('LogicalExpressionControlFlowReplacer', function () {
assert.match(obfuscatedCode, regExp);
});
});

// issue https://github.com/javascript-obfuscator/javascript-obfuscator/issues/1456
describe('prohibited nodes Variant #2: identifier as right operand', () => {
const regExp: RegExp = new RegExp(
`var ${variableMatch} *= *!${variableMatch} *&& *!${variableMatch};`
);

let obfuscatedCode: string;

before(() => {
const code: string = readFileAsString(__dirname + '/fixtures/prohibited-nodes-identifier.js');

obfuscatedCode = JavaScriptObfuscator.obfuscate(code, {
...NO_ADDITIONAL_NODES_PRESET,
controlFlowFlattening: true,
controlFlowFlatteningThreshold: 1
}).getObfuscatedCode();
});

it("shouldn't replace logical expression with identifier as right operand", () => {
assert.match(obfuscatedCode, regExp);
});
});

// issue https://github.com/javascript-obfuscator/javascript-obfuscator/issues/1456
describe('prohibited nodes Variant #3: object expression as right operand', () => {
const regExp: RegExp = new RegExp(
`var ${variableMatch} *= *${variableMatch} *&& *{'foo': *${variableMatch}};`
);

let obfuscatedCode: string;

before(() => {
const code: string = readFileAsString(__dirname + '/fixtures/prohibited-nodes-object-expression.js');

obfuscatedCode = JavaScriptObfuscator.obfuscate(code, {
...NO_ADDITIONAL_NODES_PRESET,
controlFlowFlattening: true,
controlFlowFlatteningThreshold: 1
}).getObfuscatedCode();
});

it("shouldn't replace logical expression with object expression as right operand", () => {
assert.match(obfuscatedCode, regExp);
});
});
});
});
3 changes: 1 addition & 2 deletions ...rmers/control-flow-replacers/logical-expression-control-flow-replacer/fixtures/input-3.js
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@@ -1,5 +1,4 @@
(function () {
var expression1 = true;
var expression2 = false;
var variable = !expression1 && !expression2;
var variable = !expression1 && !false;
})();
5 changes: 5 additions & 0 deletions ...eplacers/logical-expression-control-flow-replacer/fixtures/prohibited-nodes-identifier.js
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@@ -0,0 +1,5 @@
(function () {
var expression1 = true;
var expression2 = false;
var variable = !expression1 && !expression2;
})();
4 changes: 4 additions & 0 deletions ...s/logical-expression-control-flow-replacer/fixtures/prohibited-nodes-object-expression.js
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@@ -0,0 +1,4 @@
(function () {
var expression1 = true;
var variable = expression1 && {foo: expression1};
})();
1 change: 1 addition & 0 deletions test/index.spec.ts
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Expand Up @@ -92,6 +92,7 @@ import './functional-tests/issues/issue1419.spec';
import './functional-tests/issues/issue1437.spec';
import './functional-tests/issues/issue1448.spec';
import './functional-tests/issues/issue1455.spec';
import './functional-tests/issues/issue1456.spec';
import './functional-tests/javascript-obfuscator/JavaScriptObfuscator.spec';
import './functional-tests/node-transformers/control-flow-transformers/block-statement-control-flow-transformer/BlockStatementControlFlowTransformer.spec';
import './functional-tests/node-transformers/control-flow-transformers/control-flow-replacers/binary-expression-control-flow-replacer/BinaryExpressionControlFlowReplacer.spec';
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