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Cross-site Scripting occurrences in Privatebin
PrivateBin is minimalist, open source online pastebin clone where the server has zero knowledge of pasted data. In PrivateBin < v1.4.0 a cross-site scripting (XSS) vulnerability was found. The vulnerability is present in all versions from v0.21 of the project, which was at the time still called ZeroBin. The issue is caused by the fact that SVGs can contain JavaScript. This can allow an attacker to execute code, if the user opens a paste with a specifically crafted SVG attachment, and interacts with the preview image and the instance isn't protected by an appropriate content security policy. Users are advised to either upgrade to version 1.4.0 or to ensure the content security policy of their instance is set correctly. (2022-04-11, CVE-2022-24833)
In PrivateBin versions 1.2.0 before 1.2.2, and 1.3.0 before 1.3.2, a persistent XSS attack is possible. Under certain conditions, a user provided attachment file name can inject HTML leading to a persistent Cross-site scripting (XSS) vulnerability. The vulnerability has been fixed in PrivateBin v1.3.2 & v1.2.2. Admins are urged to upgrade to these versions to protect the affected users. (2020-01-23, CVE-2020-5223)
Why Cross-site Scripting can be dangerous
Cross site scripting is an attack where a web page executes code that is injected by an adversary. It usually appears, when users input is presented. This attack can be used to impersonate a user, take over control of the session, or even steal API keys.
The attack can be executed e.g. when you application injects the request parameter directly into the HTML code of the page returned to the user:
https://server.com/confirmation?message=Transaction+Complete
what results in:
<span>Confirmation: Transaction Complete</span>
In that case the message can be modified to become a valid Javascript code, e.g.:
https://server.com/confirmation?message=<script>dangerous javascript code here</script>
and it will be executed locally by the user's browser with full access to the user's personal application/browser data:
<span>Confirmation: <script>dangerous javascript code here</script></span>