Summary
Acunetix 360 detected Cross-site Scripting, which allows an attacker to execute a dynamic script (JavaScript, VBScript) in the context of the application.
The web application uses SAML. The web application's SAML Consumer Service is vulnerable to XSS due to a lack of sanitization of values from SAMLResponse. An unauthenticated attacker may be able to use it to attack other users.
Impact
Malicious JavaScript has access to all the same objects as the rest of the web page, including access to cookies and local storage, which are often used to store session tokens. If an attacker can obtain a user's session cookie, they can then impersonate that user.
Furthermore, JavaScript can read and make arbitrary modifications to the contents of a page being displayed to a user. Therefore, XSS in conjunction with some clever social engineering opens up a lot of possibilities for an attacker.
Remediation
Apply context-dependent sanitization to SAMLResponse values rendered on a page.