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[code-simplifier] Simplify runtime_import security code for better maintainability #14832

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[code-simplifier] Simplify runtime_import security code for better maintainability #14832

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54 changes: 33 additions & 21 deletions actions/setup/js/runtime_import.cjs
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Original file line number Diff line number Diff line change
Expand Up @@ -108,6 +108,37 @@ const ALLOWED_EXPRESSIONS = [
"github.workspace",
];

/**
* Dangerous JavaScript built-in property names that could be used for
* prototype pollution or prototype chain traversal attacks.
* These properties are blocked in all expressions.
*/
const DANGEROUS_PROPS = [
"constructor",
"__proto__",
"prototype",
"__defineGetter__",
"__defineSetter__",
"__lookupGetter__",
"__lookupSetter__",
"hasOwnProperty",
"isPrototypeOf",
"propertyIsEnumerable",
"toString",
"valueOf",
"toLocaleString",
];

/**
* Safely checks if an object has a property without accessing the prototype chain
* @param {any} obj - The object to check
* @param {string} prop - The property name to check
* @returns {boolean} - True if the object has the property (not inherited)
*/
function hasSafeProperty(obj, prop) {
return obj && typeof obj === "object" && Object.prototype.hasOwnProperty.call(obj, prop);
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Copilot AI Feb 10, 2026

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hasSafeProperty() can return a non-boolean falsy value due to short-circuiting (e.g., null, undefined, 0, ""). Since the JSDoc declares a boolean return and callers treat it as a predicate, wrap the expression in Boolean(...)/!! so the function always returns a real boolean.

Suggested change
return obj && typeof obj === "object" && Object.prototype.hasOwnProperty.call(obj, prop);
return Boolean(
obj && typeof obj === "object" && Object.prototype.hasOwnProperty.call(obj, prop)
);

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}

/**
* Checks if an expression is in the safe list
* @param {string} expr - The expression to check (without ${{ }})
Expand All @@ -116,23 +147,6 @@ const ALLOWED_EXPRESSIONS = [
function isSafeExpression(expr) {
const trimmed = expr.trim();

// Block dangerous JavaScript built-in property names
const DANGEROUS_PROPS = [
"constructor",
"__proto__",
"prototype",
"__defineGetter__",
"__defineSetter__",
"__lookupGetter__",
"__lookupSetter__",
"hasOwnProperty",
"isPrototypeOf",
"propertyIsEnumerable",
"toString",
"valueOf",
"toLocaleString",
];

// Split expression into parts and check each for dangerous properties
// Handle both dot notation (e.g., "github.event.issue") and bracket notation (e.g., "release.assets[0].id")
const parts = trimmed.split(/[.\[\]]+/).filter(p => p && !/^\d+$/.test(p));
Expand Down Expand Up @@ -294,8 +308,7 @@ function evaluateExpression(expr) {
if (arrayMatch) {
const key = arrayMatch[1];
const index = parseInt(arrayMatch[2], 10);
// Use Object.prototype.hasOwnProperty.call() to prevent prototype chain access
if (value && typeof value === "object" && Object.prototype.hasOwnProperty.call(value, key)) {
if (hasSafeProperty(value, key)) {
const arrayValue = value[key];
if (Array.isArray(arrayValue) && index >= 0 && index < arrayValue.length) {
value = arrayValue[index];
Expand All @@ -308,8 +321,7 @@ function evaluateExpression(expr) {
break;
}
} else {
// Use Object.prototype.hasOwnProperty.call() to prevent prototype chain access
if (value && typeof value === "object" && Object.prototype.hasOwnProperty.call(value, part)) {
if (hasSafeProperty(value, part)) {
value = value[part];
} else {
value = undefined;
Expand Down
110 changes: 40 additions & 70 deletions actions/setup/js/runtime_import.test.cjs
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Original file line number Diff line number Diff line change
Expand Up @@ -124,88 +124,58 @@ describe("runtime_import", () => {
expect(isSafeExpression("vars.SECRET || 'fallback'")).toBe(!1);
});
it("should reject OR with unsafe right side (non-literal)", () => {
expect(isSafeExpression("inputs.value || secrets.TOKEN")).toBe(!1);
expect(isSafeExpression("github.actor || vars.NAME")).toBe(!1);
expect(isSafeExpression("inputs.value || secrets.TOKEN")).toBe(false);
expect(isSafeExpression("github.actor || vars.NAME")).toBe(false);
});
it("should block dangerous property names - constructor", () => {
expect(isSafeExpression("github.constructor")).toBe(!1);
expect(isSafeExpression("inputs.constructor")).toBe(!1);
expect(isSafeExpression("github.event.constructor")).toBe(!1);
expect(isSafeExpression("needs.job.constructor")).toBe(!1);
});
it("should block dangerous property names - __proto__", () => {
expect(isSafeExpression("github.__proto__")).toBe(!1);
expect(isSafeExpression("inputs.__proto__")).toBe(!1);
expect(isSafeExpression("github.event.__proto__")).toBe(!1);
});
it("should block dangerous property names - prototype", () => {
expect(isSafeExpression("github.prototype")).toBe(!1);
expect(isSafeExpression("inputs.prototype")).toBe(!1);
expect(isSafeExpression("github.event.prototype")).toBe(!1);
});
it("should block dangerous property names - __defineGetter__", () => {
expect(isSafeExpression("github.__defineGetter__")).toBe(!1);
expect(isSafeExpression("inputs.__defineGetter__")).toBe(!1);
});
it("should block dangerous property names - __defineSetter__", () => {
expect(isSafeExpression("github.__defineSetter__")).toBe(!1);
expect(isSafeExpression("inputs.__defineSetter__")).toBe(!1);
});
it("should block dangerous property names - __lookupGetter__", () => {
expect(isSafeExpression("github.__lookupGetter__")).toBe(!1);
expect(isSafeExpression("inputs.__lookupGetter__")).toBe(!1);
});
it("should block dangerous property names - __lookupSetter__", () => {
expect(isSafeExpression("github.__lookupSetter__")).toBe(!1);
expect(isSafeExpression("inputs.__lookupSetter__")).toBe(!1);
});
it("should block dangerous property names - hasOwnProperty", () => {
expect(isSafeExpression("github.hasOwnProperty")).toBe(!1);
expect(isSafeExpression("inputs.hasOwnProperty")).toBe(!1);
});
it("should block dangerous property names - isPrototypeOf", () => {
expect(isSafeExpression("github.isPrototypeOf")).toBe(!1);
expect(isSafeExpression("inputs.isPrototypeOf")).toBe(!1);
});
it("should block dangerous property names - propertyIsEnumerable", () => {
expect(isSafeExpression("github.propertyIsEnumerable")).toBe(!1);
expect(isSafeExpression("inputs.propertyIsEnumerable")).toBe(!1);
});
it("should block dangerous property names - toString", () => {
expect(isSafeExpression("github.toString")).toBe(!1);
expect(isSafeExpression("inputs.toString")).toBe(!1);
});
it("should block dangerous property names - valueOf", () => {
expect(isSafeExpression("github.valueOf")).toBe(!1);
expect(isSafeExpression("inputs.valueOf")).toBe(!1);
});
it("should block dangerous property names - toLocaleString", () => {
expect(isSafeExpression("github.toLocaleString")).toBe(!1);
expect(isSafeExpression("inputs.toLocaleString")).toBe(!1);
});
it("should block dangerous properties in array access", () => {
expect(isSafeExpression("github.event.release.assets[0].constructor")).toBe(!1);
expect(isSafeExpression("github.event.release.assets[0].__proto__")).toBe(!1);
it("should block dangerous property names", () => {
const dangerousProps = [
"constructor",
"__proto__",
"prototype",
"__defineGetter__",
"__defineSetter__",
"__lookupGetter__",
"__lookupSetter__",
"hasOwnProperty",
"isPrototypeOf",
"propertyIsEnumerable",
"toString",
"valueOf",
"toLocaleString",
];

for (const prop of dangerousProps) {
expect(isSafeExpression(`github.${prop}`)).toBe(false);
expect(isSafeExpression(`inputs.${prop}`)).toBe(false);
expect(isSafeExpression(`github.event.${prop}`)).toBe(false);
}

// Additional tests for constructor
expect(isSafeExpression("needs.job.constructor")).toBe(false);

// Tests for dangerous properties in array access
expect(isSafeExpression("github.event.release.assets[0].constructor")).toBe(false);
expect(isSafeExpression("github.event.release.assets[0].__proto__")).toBe(false);
});
it("should reject excessive nesting depth (more than 5 levels)", () => {
// Valid: max 5 levels (needs.job.outputs.foo.bar)
expect(isSafeExpression("needs.job.outputs.foo.bar")).toBe(!0);
expect(isSafeExpression("steps.step.outputs.foo.bar")).toBe(!0);
expect(isSafeExpression("needs.job.outputs.foo.bar")).toBe(true);
expect(isSafeExpression("steps.step.outputs.foo.bar")).toBe(true);
// Invalid: 6 levels
expect(isSafeExpression("needs.job.outputs.foo.bar.baz")).toBe(!1);
expect(isSafeExpression("steps.step.outputs.foo.bar.baz")).toBe(!1);
expect(isSafeExpression("needs.job.outputs.foo.bar.baz")).toBe(false);
expect(isSafeExpression("steps.step.outputs.foo.bar.baz")).toBe(false);
// Invalid: 7+ levels
expect(isSafeExpression("needs.job.outputs.foo.bar.baz.qux")).toBe(!1);
expect(isSafeExpression("needs.job.outputs.foo.bar.baz.qux")).toBe(false);
});
it("should allow valid nested expressions within depth limit", () => {
// 2 levels
expect(isSafeExpression("needs.job.outputs")).toBe(!0);
expect(isSafeExpression("needs.job.outputs")).toBe(true);
// 3 levels
expect(isSafeExpression("needs.job.outputs.result")).toBe(!0);
expect(isSafeExpression("needs.job.outputs.result")).toBe(true);
// 4 levels
expect(isSafeExpression("needs.job.outputs.foo.value")).toBe(!0);
expect(isSafeExpression("needs.job.outputs.foo.value")).toBe(true);
// 5 levels (max)
expect(isSafeExpression("needs.job.outputs.foo.bar")).toBe(!0);
expect(isSafeExpression("needs.job.outputs.foo.bar")).toBe(true);
});
}),
describe("evaluateExpression", () => {
Expand Down
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