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fix(captcha): prevent injection of malicious payloads in challenge.image #1652

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fix(captcha): prevent injection of malicious payloads in challenge.image #1652

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6f59d19
fix(captcha): prevent injection of malicious payloads in challenge.image
amitsingh05667 May 19, 2026
142ab56
fix
amitsingh05667 May 19, 2026
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10 changes: 7 additions & 3 deletions src/web-auth/captcha.js
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Original file line number Diff line number Diff line change
Expand Up @@ -33,9 +33,7 @@ var defaults = {
: 'Solve the formula shown above';
return (
'<div class="captcha-challenge">\n' +
' <img src="' +
challenge.image +
'" />\n' +
' <img src="" />\n' +
' <button type="button" class="captcha-reload">↺</button>\n' +
'</div>\n' +
'<input type="text" name="captcha"\n' +
Expand Down Expand Up @@ -71,6 +69,12 @@ var defaults = {

function handleAuth0Provider(element, options, challenge, load) {
element.innerHTML = options.templates[challenge.provider](challenge);
// Use setAttribute to safely assign challenge.image — avoids HTML injection via innerHTML string concat.
// If a custom template is used that omits .captcha-challenge img, src will not be set (by design).
var img = element.querySelector('.captcha-challenge img');
if (img) {
img.setAttribute('src', challenge.image || '');
}
element
.querySelector('.captcha-reload')
.addEventListener('click', function (e) {
Expand Down
36 changes: 36 additions & 0 deletions test/web-auth/captcha.test.js
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Original file line number Diff line number Diff line change
Expand Up @@ -123,6 +123,18 @@ describe('captcha rendering', function () {
expect(imgEl.src).to.equal(challenges[0].image);
});

it('should not inject HTML attributes when challenge.image contains a malicious payload', function () {
const { window: w } = new JSDOM('<body><div class="captcha" style="display: none;" /></body>');
const el = w.document.querySelector('.captcha');
const maliciousChallenge = { required: true, provider: 'auth0', image: 'x" onerror="alert(1)" x="' };
const mockClient = { getChallenge: cb => cb(null, maliciousChallenge) };
captcha.render(mockClient, captcha.Flow.DEFAULT, el, {});
const imgEl = el.querySelector('img');
expect(imgEl).to.be.ok();
expect(imgEl.getAttribute('onerror')).to.equal(null);
expect(imgEl.getAttribute('src')).to.equal(maliciousChallenge.image);
});

it('should contain an input tag with name captcha', function () {
const inputEl = element.querySelector('input[name="captcha"]');
expect(inputEl).to.be.ok();
Expand Down Expand Up @@ -762,6 +774,18 @@ describe('passwordless captcha rendering', function () {
expect(imgEl.src).to.equal(challenges[0].image);
});

it('should not inject HTML attributes when challenge.image contains a malicious payload', function () {
const { window: w } = new JSDOM('<body><div class="captcha" style="display: none;" /></body>');
const el = w.document.querySelector('.captcha');
const maliciousChallenge = { required: true, provider: 'auth0', image: 'x" onerror="alert(1)" x="' };
const mockClient = { passwordless: { getChallenge: cb => cb(null, maliciousChallenge) } };
captcha.render(mockClient, captcha.Flow.PASSWORDLESS, el, {});
const imgEl = el.querySelector('img');
expect(imgEl).to.be.ok();
expect(imgEl.getAttribute('onerror')).to.equal(null);
expect(imgEl.getAttribute('src')).to.equal(maliciousChallenge.image);
});

it('should contain an input tag with name captcha', function () {
const inputEl = element.querySelector('input[name="captcha"]');
expect(inputEl).to.be.ok();
Expand Down Expand Up @@ -1378,6 +1402,18 @@ describe('password reset captcha rendering', function () {
expect(imgEl.src).to.equal(challenges[0].image);
});

it('should not inject HTML attributes when challenge.image contains a malicious payload', function () {
const { window: w } = new JSDOM('<body><div class="captcha" style="display: none;" /></body>');
const el = w.document.querySelector('.captcha');
const maliciousChallenge = { required: true, provider: 'auth0', image: 'x" onerror="alert(1)" x="' };
const mockClient = { dbConnection: { getPasswordResetChallenge: cb => cb(null, maliciousChallenge) } };
captcha.render(mockClient, captcha.Flow.PASSWORD_RESET, el, {});
const imgEl = el.querySelector('img');
expect(imgEl).to.be.ok();
expect(imgEl.getAttribute('onerror')).to.equal(null);
expect(imgEl.getAttribute('src')).to.equal(maliciousChallenge.image);
});

it('should contain an input tag with name captcha', function () {
const inputEl = element.querySelector('input[name="captcha"]');
expect(inputEl).to.be.ok();
Expand Down