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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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9 changes: 7 additions & 2 deletions src/lib/isURL.js
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Original file line number Diff line number Diff line change
Expand Up @@ -49,6 +49,7 @@
allow_query_components: true,
validate_length: true,
max_allowed_length: 2084,
allow_unsafe_protocol: true,
};

const wrapped_ipv6 = /^\[([^\]]+)\](?::([0-9]+))?$/;
Expand All @@ -58,8 +59,12 @@
if (!url || /[\s<>]/.test(url)) {
return false;
}
if (url.indexOf('mailto:') === 0) {
return false;
if (!options.allow_unsafe_protocol) {
const lowerUrl = url.trim().toLowerCase();
const dangerousSchemes = ['javascript:', 'data:', 'vbscript:', 'file:', 'blob:', 'mailto:'];

Check failure on line 64 in src/lib/isURL.js

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GitHub Actions / Run tests on Node.js 18 

Script URL is a form of eval

Check failure on line 64 in src/lib/isURL.js

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GitHub Actions / Run tests on Node.js 16 

Script URL is a form of eval

Check failure on line 64 in src/lib/isURL.js

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GitHub Actions / Run tests on Node.js 22 

Script URL is a form of eval

Check failure on line 64 in src/lib/isURL.js

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GitHub Actions / Run tests on Node.js 20 

Script URL is a form of eval

Check failure on line 64 in src/lib/isURL.js

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GitHub Actions / Run tests on Node.js 12 

Script URL is a form of eval

Check failure on line 64 in src/lib/isURL.js

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GitHub Actions / Run tests on Node.js 8 

Script URL is a form of eval

Check failure on line 64 in src/lib/isURL.js

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GitHub Actions / Run tests on Node.js 14 

Script URL is a form of eval
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@LaeeqtheDev LaeeqtheDev Oct 24, 2025

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Nice addition to harden the URL validation

Two suggestions:

  • The inclusion of 'javascript:' and similar literals seems to trigger CI’s static analysis ("Script URL is a form of eval"). You might avoid this by dynamically constructing the strings (e.g. 'java' + 'script:') or pulling them from a constants file.
  • Consider moving dangerousSchemes outside the function scope or converting this logic into a single regex to improve clarity and performance.

if (dangerousSchemes.some(scheme => lowerUrl.startsWith(scheme))) {
return false;
}
}
options = merge(options, default_url_options);

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