CVE-2021-1566

What it is

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.

At a glance

Exploitability

Can be exploited over the network without logging in. High risk of data exposure, data tampering.

Exploit odds

0.7% chance of exploitation in the next 30 days (EPSS).

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2021-06-16 18:15 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-06-17 03:32 UTC Last updatedMost recent change to the record

Why it ranks here

• Exploited in the wild: no, CISA does not list it.
• Exploit odds: 0.7% in the next 30 days (EPSS).
• Severity: 7.4 HIGH (CVSS).
• Fix: a patch or advisory is linked.

Details

Published

2021-06-16 18:15 UTC

Last modified

2026-06-17 03:32 UTC

Exploit probability

0.7% · EPSS, next 30 days

Weakness

CWE-296

Record status

Modified

Affected

• Cisco Email Security Appliance
• Cisco Asyncos < 12.5.3-035
• Cisco Asyncos < 13.0.0-030
• Cisco Asyncos < 13.5.3-010
• Cisco Web Security Appliance
• Cisco Asyncos < 11.8.3-021
• Cisco Asyncos < 12.0.3-005
• Cisco Asyncos < 12.5.1-043

Attack profile CVSS 3.1 · 7.4

Attack vector

Network

Complexity

High

Privileges needed

None

User interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

High

Availability

None

Is it in your code?

Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.

Read https://cve-list.com/agent/cve/CVE-2021-1566.md and follow it. Check whether this project is affected by CVE-2021-1566. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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