CVE-2020-3580

CVE-2020-3580 is a cross-site scripting (XSS) flaw caused by insufficient validation of user-supplied input in the web services interface of Cisco ASA and Firepower Threat Defense (FTD) software. An unauthenticated, remote attacker can exploit it by persuading a user of the web interface to click a crafted link, which then executes arbitrary script code in the context of the interface or exposes sensitive browser-based information such as session data. Only devices running specific AnyConnect and WebVPN configurations are affected, so not every ASA/FTD deployment is vulnerable. The flaw is under active exploitation: it is in CISA's Known Exploited Vulnerabilities catalog (added 2021-11-03) with known ransomware use, a public PoC exploit has driven scanning, and groups such as Akira and LockBit are actively searching for vulnerable Cisco ASA devices.

What to do: Apply updates per the vendor's instructions (Cisco's advisory lists the fixed ASA/FTD releases), prioritizing internet-facing devices since ransomware operators (Akira, LockBit) are actively scanning. Check whether the web services interface (AnyConnect/WebVPN) is enabled, as only those configurations are vulnerable, and restrict internet access to the device's management/web interface where possible. Treat as urgent given its KEV listing and known ransomware use.