CVE-2021-43808: Blade `@parent` Exploitation Leading To Possible XSS in Laravel
First published: Tue Dec 07 2021(Updated: )
A security researcher has disclosed a possible XSS vulnerability in the Blade templating engine. Given the following two Blade templates: resources/views/parent.blade.php: ```html @section('content') <input value="{{ $value }}"> @show ``` resources/views/child.blade.php: ```html @extends('parent') @section('content') <input value="{{ $value }}"> @endsection ``` And a route like the following: ```php Route::get('/example', function() { $value = '//localhost/###parent-placeholder-040f06fd774092478d450774f5ba30c5da78acc8## onclick=location.assign(this.value);//'; return view('child', ['value' => $value]); }); ``` The broken HTML element may be clicked and the user is taken to another location in their browser due to XSS. This is due to the user being able to guess the parent placeholder SHA-1 hash by trying common names of sections. If the parent template contains an exploitable HTML structure an XSS vulnerability can be exposed. This vulnerability has been patched by determining the parent placeholder at runtime and using a random hash that is unique to each request.
Credit: security-advisories@github.com security-advisories@github.com
| Affected Software | Affected Version | How to fix |
|---|---|---|
| composer/illuminate/view | <6.20.42>=7.0.0<7.30.6>=8.0.0<8.75.0 | |
| composer/laravel/framework | <6.20.42>=7.0.0<7.30.6>=8.0.0<8.75.0 | |
| Laravel Framework | <6.20.42 | |
| Laravel Framework | >=7.0.0<7.30.6 | |
| Laravel Framework | >=8.0.0<8.75.0 | |
| composer/illuminate/view | >=8.0.0<8.75.0 | 8.75.0 |
| composer/illuminate/view | >=7.0.0<7.30.6 | 7.30.6 |
| composer/illuminate/view | <6.20.42 | 6.20.42 |
| composer/laravel/framework | >=8.0.0<8.75.0 | 8.75.0 |
| composer/laravel/framework | >=7.0.0<7.30.6 | 7.30.6 |
| composer/laravel/framework | <6.20.42 | 6.20.42 |
| <6.20.42 | ||
| >=7.0.0<7.30.6 | ||
| >=8.0.0<8.75.0 |
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Reference Links
- https://github.com/laravel/framework/security/advisories/GHSA-66hf-2p6w-jqfw
- https://github.com/laravel/framework/commit/b8174169b1807f36de1837751599e2828ceddb9b
- https://github.com/laravel/framework/pull/39906
- https://github.com/laravel/framework/pull/39908
- https://github.com/laravel/framework/pull/39909
- https://github.com/laravel/framework/releases/tag/v6.20.42
- https://github.com/laravel/framework/releases/tag/v7.30.6
- https://github.com/laravel/framework/releases/tag/v8.75.0
- https://nvd.nist.gov/vuln/detail/CVE-2021-43808
- https://github.com/FriendsOfPHP/security-advisories/blob/master/illuminate/view/CVE-2021-43808.yaml
- https://github.com/FriendsOfPHP/security-advisories/blob/master/laravel/framework/CVE-2021-43808.yaml
- https://github.com/advisories/GHSA-66hf-2p6w-jqfw (Advisory)
Frequently Asked Questions
What is CVE-2021-43808?
CVE-2021-43808 is a possible cross-site scripting (XSS) vulnerability in the Blade templating engine in Laravel prior to versions 8.75.0, 7.30.6, and 6.20.42.
How can a broken HTML element be exploited in the XSS vulnerability?
A broken HTML element may be clicked and the user taken to another location in their browser due to XSS.
Which versions of Laravel are affected by CVE-2021-43808?
Laravel versions prior to 8.75.0, 7.30.6, and 6.20.42 are affected by CVE-2021-43808.
What is the severity of CVE-2021-43808?
CVE-2021-43808 has a severity score of 6.1, which is considered medium.
How can I fix the XSS vulnerability in Laravel?
To fix the XSS vulnerability in Laravel, update to version 8.75.0, 7.30.6, or 6.20.42 or later.
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