AEM's Cloud Service offering, as well as versions 6.5.7.0 (and below), 6.4.8.3 (and below) and 6.3.3.8 (and below) are affected by a stored Cross-Site Scripting (XSS) vulnerability that could be abused by an attacker to inject malicious scripts into vulnerable form fields. Malicious JavaScript may be executed in a victim’s browser when they browse to the page containing the vulnerable field.
https://helpx.adobe.com/security/products/experience-manager/apsb21-15.html