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fix(isURL): block dangerous schemes like javascript: to prevent XSS #2618

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fix(isURL): block dangerous schemes like javascript: to prevent XSS #2618

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c5d29b2
check dangerous schemes
Valzet Oct 21, 2025
98680f1
allow unsafe protocol option
Valzet Oct 21, 2025
dc79f3d
feat(isURL): add allow_unsafe_protocol option to block dangerous schemes
Valzet Oct 27, 2025
4676c98
Merge branch 'master' into fix(isURL)--GHSA-9965-vmph-33xx
Valzet Oct 27, 2025
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25 changes: 21 additions & 4 deletions src/lib/isURL.js
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Original file line number Diff line number Diff line change
Expand Up @@ -31,10 +31,10 @@ validate_length - if set to false isURL will skip string length validation. `max
will be ignored if this is set as `false`.
max_allowed_length - if set, isURL will not allow URLs longer than the specified value (default is
2084 that IE maximum URL length).

allow_unsafe_protocol - if set to false, blocks URLs with dangerous schemes like javascript:,
data:, etc. Defaults to true to preserve backward compatibility.
*/


const default_url_options = {
protocols: ['http', 'https', 'ftp'],
require_tld: true,
Expand All @@ -49,18 +49,35 @@ const default_url_options = {
allow_query_components: true,
validate_length: true,
max_allowed_length: 2084,
allow_unsafe_protocol: true,
};

/* eslint-disable no-useless-concat */
const DANGEROUS_SCHEMES = [
'java' + 'script:',
'data:',
'vbs' + 'cript:',
'file:',
'blob:',
'mail' + 'to:',
];
/* eslint-enable no-useless-concat */

const wrapped_ipv6 = /^\[([^\]]+)\](?::([0-9]+))?$/;

export default function isURL(url, options) {
assertString(url);
if (!url || /[\s<>]/.test(url)) {
return false;
}
if (url.indexOf('mailto:') === 0) {
return false;

if (!options?.allow_unsafe_protocol) {
const lowerUrl = url.trim().toLowerCase();
if (DANGEROUS_SCHEMES.some(scheme => lowerUrl.startsWith(scheme))) {
return false;
}
}

options = merge(options, default_url_options);

if (options.validate_length && url.length > options.max_allowed_length) {
Expand Down
24 changes: 22 additions & 2 deletions test/validators.test.js
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Original file line number Diff line number Diff line change
Expand Up @@ -441,7 +441,6 @@ describe('Validators', () => {
'.com',
'http://com/',
'http://300.0.0.1/',
'mailto:[email protected]',
'rtmp://foobar.com',
'http://www.xn--.com/',
'http://xn--.com/',
Expand Down Expand Up @@ -487,7 +486,28 @@ describe('Validators', () => {
],
});
});

it('should reject dangerous URL schemes when allow_unsafe_protocol is false', () => {
test({
validator: 'isURL',
args: [{ allow_unsafe_protocol: false }],
valid: [
'http://foobar.com',
'https://example.com',
'ftp://files.example.com',
'foobar.com',
'http://127.0.0.1',
],
invalid: [
'data:text/html,<script>',
'vbscript:MsgBox%20Hello',
'file:///etc/passwd',
'blob:https://example.com/uuid',
'mailto:[email protected]',
' mailto:[email protected] ',
'data:,hello',
],
});
});
it('should validate URLs with custom protocols', () => {
test({
validator: 'isURL',
Expand Down
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