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Cross-site Scripting occurrences in Enterprise Security Api
ESAPI (The OWASP Enterprise Security API) is a free, open source, web application security control library. Prior to version 2.3.0.0, there is a potential for a cross-site scripting vulnerability in ESAPI caused by a incorrect regular expression for "onsiteURL" in the **antisamy-esapi.xml** configuration file that can cause "javascript:" URLs to fail to be correctly sanitized. This issue is patched in ESAPI 2.3.0.0. As a workaround, manually edit the **antisamy-esapi.xml** configuration files to change the "onsiteURL" regular expression. More information about remediation of the vulnerability, including the workaround, is available in the maintainers' release notes and security bulletin. (2022-04-27, CVE-2022-24891)
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>