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🐛 Anchor ALLOWED_FONT_REGEX in a4a head validation #40530

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🐛 Anchor ALLOWED_FONT_REGEX in a4a head validation #40530

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11 changes: 8 additions & 3 deletions extensions/amp-a4a/0.1/head-validation.js
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Original file line number Diff line number Diff line change
Expand Up @@ -17,9 +17,13 @@ import {getMode} from '../../../src/mode';
*/
export let ValidatedHeadDef;

// From validator/validator-main.protoascii
// From validator/validator-main.protoascii. The validator matches this against
// the whole attribute value (RE2::FullMatch), so anchor it here too: RegExp.test
// is a substring match, which would accept any href that merely contains an
// allowed provider (e.g. https://evil.example/#https://fast.fonts.net/).
const ALLOWED_FONT_REGEX = new RegExp(
'https://cdn\\.materialdesignicons\\.com/' +
'^(?:' +
'https://cdn\\.materialdesignicons\\.com/' +
'([0-9]+\\.?)+/css/materialdesignicons\\.min\\.css|' +
'https://cloud\\.typography\\.com/' +
'[0-9]*/[0-9]*/css/fonts\\.css|' +
Expand All @@ -32,7 +36,8 @@ const ALLOWED_FONT_REGEX = new RegExp(
'https://(use|pro)\\.fontawesome\\.com/releases/v([0-9]+\\.?)+' +
'/css/[0-9a-zA-Z-]+\\.css|' +
'https://(use|pro)\\.fontawesome\\.com/[0-9a-zA-Z-]+\\.css|' +
'https://use\\.typekit\\.net/[\\w\\p{L}\\p{N}_]+\\.css'
'https://use\\.typekit\\.net/[\\w\\p{L}\\p{N}_]+\\.css' +
')$'
);

// If editing please also change:
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13 changes: 13 additions & 0 deletions extensions/amp-a4a/0.1/test/test-head-validation.js
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Original file line number Diff line number Diff line change
Expand Up @@ -187,6 +187,19 @@ describes.realWin('head validation', {amp: true}, (env) => {
expect(preloadStub).not.to.be.called;
});

it('does not allow a foreign origin that embeds an allowlisted provider substring', () => {
const preloadStub = env.sandbox.stub(
Services.preconnectFor(env.win),
'preload'
);
head.innerHTML = `
<link href="https://evil.example/x.css#https://fast.fonts.net/" rel="stylesheet">
`;
const validated = processHead(env.win, adElement, head);
expect(validated.head.querySelector('link')).not.to.exist;
expect(preloadStub).not.to.be.called;
});

it('keeps amp styles', () => {
head.innerHTML = `
<style amp-custom></style>
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