CVE-2021-21800: 
Advantech R-SeeNet vulnerability analysis and mitigation

A cross-site scripting (XSS) vulnerability exists in the sshform.php script functionality of Advantech R-SeeNet v 2.4.12 (20.10.2020). The vulnerability allows an attacker to execute arbitrary JavaScript code in the context of the targeted user's browser when a user visits a specially crafted URL ([Talos Report](https://talosintelligence.com/vulnerabilityreports/TALOS-2021-1271)).

The vulnerability exists in the sshform.php script, which is part of the Advantech R-SeeNet web applications. The script accepts a 'hostname' parameter via HTTP request without proper sanitization in the context of XSS payload. The parameter is then embedded directly into HTML code, allowing for script injection. The vulnerability has been assigned a CVSSv3 score of 9.6 (CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H) and is classified as CWE-79 (Improper Neutralization of Input During Web Page Generation) ([Talos Report](https://talosintelligence.com/vulnerabilityreports/TALOS-2021-1271)).

If exploited, this vulnerability allows attackers to execute arbitrary JavaScript code in the context of the targeted user's browser. The victim does not need to be logged in to be affected by this vulnerability. Given the high CVSS score of 9.6, this vulnerability poses significant risks to confidentiality, integrity, and availability of the affected systems (Talos Report).

The vulnerability was disclosed to the vendor on March 11, 2021, with follow-ups on April 13 and June 7, 2021. After no response from the vendor within the 90-day disclosure deadline, the vulnerability was publicly disclosed on July 15, 2021. No official patch was available at the time of disclosure (Talos Report).