CVE-2021-21799: 
Advantech R-SeeNet vulnerability analysis and mitigation

Cross-site scripting vulnerabilities exist in the telnetform.php script functionality of Advantech R-SeeNet v 2.4.12 (20.10.2020). The vulnerability was discovered in early 2021 and publicly disclosed on July 15, 2021. The affected software, R-SeeNet, is a monitoring system used for Advantech routers that continuously collects information from individual routers in the network and records the data into a SQL database ([Talos Report](https://talosintelligence.com/vulnerabilityreports/TALOS-2021-1270)).

The vulnerability exists in the telnetform.php script, which accepts a hostname parameter via HTTP GET request. The parameter is not properly sanitized for XSS payload before being embedded into HTML code. The vulnerability has been assigned CWE-79 (Improper Neutralization of Input During Web Page Generation) and received a CVSS v3.0 score of 9.6 CRITICAL (CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H) ([Talos Report](https://talosintelligence.com/vulnerabilityreports/TALOS-2021-1270)).

If exploited, this vulnerability allows an attacker 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 CVSS score of 9.6, this indicates potential for high impact on confidentiality, integrity, and availability of the system (Talos Report).

The vulnerability was reported to the vendor on March 11, 2021, followed by multiple follow-ups. After no response from the vendor within the 90-day disclosure period, the vulnerability was publicly disclosed on July 15, 2021. No official patch or mitigation was provided by Advantech (Talos Report).