CVE-2021-1566 Cisco Email Security Appliance and Cisco Web Security Appliance Certificate Validation Vulnerability
A man-in-the-middle attacker can bypass TLS certificate validation to intercept traffic, extract sensitive information, or alter API requests on Cisco security appliances.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2021-1566?
CVE-2021-1566 is a high-severity vulnerability in Cisco Asyncos, published on 16 Jun 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
A vulnerability in the Cisco Advanced Malware Protection (AMP) for Endpoints integration of Cisco AsyncOS for Cisco Email Security Appliance (ESA) and Cisco Web Security Appliance (WSA) could allow an unauthenticated, remote attacker to intercept traffic between an affected device and the AMP servers. This vulnerability is due to improper certificate validation when an affected device establishes TLS connections. A man-in-the-middle attacker could exploit this vulnerability by sending a crafted TLS packet to an affected device. A successful exploit could allow the attacker to spoof a trusted host and then extract sensitive information or alter certain API requests.
Which versions are affected by CVE-2021-1566?
It affects 3 products.
Products include Cisco Asyncos, Cisco Email Security Appliance, Cisco Web Security Appliance.
How do I fix CVE-2021-1566?
No fix has been published for CVE-2021-1566 yet. Limit exposure of the affected software until one is available.
Is CVE-2021-1566 being exploited?
There is no known exploitation of CVE-2021-1566 in the wild and no public exploit code.
Other vulnerabilities in Cisco Asyncos
- CVE-2025-20393 Cisco Multiple Products Improper Input Validation
- CVE-2026-76519 Cisco Secure Email Gateway Relative Path Traversal
- CVE-2026-76461 Cisco Secure Email Gateway SQL Injection
- CVE-2024-20435 Command injection in Cisco Secure Web Appliance
- CVE-2019-15956 Cisco Web Security Appliance Unauthorized Device Reset Vulnerability
Sources
Also known as GHSA-9pg8-7479-p4jw.