Cisco ASA and FTD Cross-Site Scripting (XSS) Vulnerability

Exploited · KEV 2021-11-03RansomwareCVE-2020-3580CWE-79

Exploited since 2021-11-03. No WAF vendor names it yet. Our CRS test: blocked.

Edge rules

0/8

Our test

Blocked

CVSS

6.1

EPSS

85.6% Top 0.3%

Posts, 14d

Published

2020-10-21

Multiple vulnerabilities in the web services interface of Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to conduct cross-site scripting (XSS) attacks against a user of the web services interface of an affected device. The vulnerabilities are due to insufficient validation of user-supplied input by the web services interface of an affected device. An attacker could exploit these vulnerabilities by persuading a user of the interface to click a crafted link. A successful exploit could allow the attacker to execute arbitrary script code in the context of the interface or allow the attacker to access sensitive, browser-based information. Note: These vulnerabilities affect only specific AnyConnect and WebVPN configurations. For more information, see the Vulnerable Products section.

Edge coverage

Claimed by vendors

CloudflareBefore feed historyOlder than its feedEnterprise: blocked · Free: passed AWSNo public claimNot namedWe measured: blocked Microsoft AzureNo public claimNot named Google CloudBefore feed historyOlder than its feedWe measured: blocked FastlyBefore feed historyOlder than its feed F5Before feed historyOlder than its feed AkamaiNo public sourceNo public changelog OWASP CRSBefore feed historyOlder than its feed

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Ask about CVE-2020-3580: who's covered, what to patch first, how vendors compare. I cite sources and won't help with attacks.

Workers AI (Llama 3.3). Can be wrong: check the cited source.

Severity, decoded

CVSS 3.1

6.1Medium

Medium · 6.1 / 10

Exploitable over the network, with no privileges and user interaction, leading to low impact on confidentiality and integrity, and the impact can reach components beyond the vulnerable one.

Over the internetNo login neededNeeds a user to actWorks reliablySpreads beyond the app

How the score is built8 metrics

Attack vectorAn attacker can reach it over the internet; no access to your network needed.
Network
Attack complexityNo special conditions are needed; the attack works reliably.
Low
Privileges requiredNo account or login is needed.
None
User interactionA user has to do something first, such as open a file or click a link.
Required
ScopeThe attack can spread beyond the vulnerable component to other parts of the system.
Changed
Confidentiality impactAn attacker can read some data, but has no control over what they get.
Low
Integrity impactAn attacker can change some data, but with limited control or limited effect.
Low
Availability impactThe component keeps working normally.
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

CISA's assessmentSSVC, from the CVE record

ExploitationActive

Attackers are exploiting this in the wild.

AutomatableNo

At least one step needs hands-on work, which slows mass attacks.

Technical impactPartial

A successful attack gives limited control over the affected software or limited access to its data.

Public exploits

1 found

0 Metasploit0 Exploit-DB1 Scanner template0 GitHub PoCs

NucleiCVE-2020-3580.yamldetection template, replayed in our lab

Links are to third-party code: never run it outside an isolated lab.

Timeline

2020-10-21
CVE published
CVE List
2021-11-03
Added to CISA KEV
Confirmed exploitation in the wild
2026-11-02
Our test: OWASP Core Rule Set blocked it
paranoia level 1, anomaly threshold 5, default CRS settings
2026-11-02
Our test: OWASP Core Rule Set blocked it
paranoia level 2, anomaly threshold 5, default CRS settings