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security: validate PERCY_SERVER_ADDRESS to loopback (PER-8681, PER-8682) #1165

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security: validate PERCY_SERVER_ADDRESS to loopback (PER-8681, PER-8682) #1165

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34 changes: 31 additions & 3 deletions addon-test-support/@percy/ember/index.js
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Original file line number Diff line number Diff line change
Expand Up @@ -10,8 +10,33 @@ const ENV_INFO = [`ember/${emberVersion}`];
if (window.QUnit) ENV_INFO.push(`qunit/${window.QUnit.version}`);
if (window.mocha) ENV_INFO.push(`mocha/${window.mocha.version}`);

// Maybe set the CLI API address from the environment
utils.percy.address = SDKENV.PERCY_SERVER_ADDRESS;
// The Percy CLI always runs locally, so its address must resolve to a loopback
// host. Accepting an arbitrary PERCY_SERVER_ADDRESS would let an attacker who
// can set it redirect snapshot/healthcheck traffic — and, critically, the
// @percy/dom bundle that is eval'd below is fetched from this address — to a
// hostile host, turning the eval into remote code execution in the test browser
// (CWE-918 / CWE-94 — PER-8681 / PER-8682).
const LOOPBACK_HOSTS = new Set(['localhost', '127.0.0.1', '::1', '[::1]']);

function isLoopbackAddress(address) {
try {
return LOOPBACK_HOSTS.has(new URL(address).hostname.toLowerCase());
} catch (e) {
return false;
}
}

// Maybe set the CLI API address from the environment (loopback only)
if (SDKENV.PERCY_SERVER_ADDRESS) {
if (isLoopbackAddress(SDKENV.PERCY_SERVER_ADDRESS)) {
utils.percy.address = SDKENV.PERCY_SERVER_ADDRESS;
} else {
utils.logger('ember').warn(
`Ignoring non-loopback PERCY_SERVER_ADDRESS "${SDKENV.PERCY_SERVER_ADDRESS}"; ` +
'the Percy CLI must run on localhost.'
);
}
}

// Helper to generate a snapshot name from the test suite
function generateName(assertOrTestOrName) {
Expand Down Expand Up @@ -69,7 +94,10 @@ export default async function percySnapshot(name, {
name = generateName(name);

try {
// Inject @percy/dom
// Inject @percy/dom. fetchPercyDOM() retrieves the bundle from
// utils.percy.address, which is now validated to a loopback host at module
// load (see above), so this eval only ever executes code served by the
// local Percy CLI rather than an attacker-controlled origin (PER-8682).
if (!window.PercyDOM) {
// eslint-disable-next-line no-eval
eval(await utils.fetchPercyDOM());
Expand Down
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