CVE-2021-1566Network attack vector

Traffic interception via improper TLS certificate validation

Published Jun 16, 2021 · Updated Nov 7, 2024

Improper certificate validation in Cisco Secure Web Appliance allows man-in-the-middle attackers to read or alter AMP API traffic. The AMP for Endpoints integration accepts a crafted TLS packet without properly validating the server certificate chain, allowing a spoofed host to impersonate an AMP server. The appliance must run an affected AsyncOS release with AMP console integration enabled, and the attacker must intercept its AMP server connection.

CVSS severity7.4
High
EPSS probability0.67%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Improper certificate validation in Cisco Secure Web Appliance allows man-in-the-middle attackers to read or alter AMP API traffic. The AMP for Endpoints integration accepts a crafted TLS packet without properly validating the server certificate chain, allowing a spoofed host to impersonate an AMP server. The appliance must run an affected AsyncOS release with AMP console integration enabled, and the attacker must intercept its AMP server connection.

The record

CVE
CVE-2021-1566
Published
Jun 16, 2021
Updated
Nov 7, 2024
Vendor
ClamAV
Product
Cisco Secure Web Appliance
Classifications
CWE-296, CWE-295, T1557
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 16, 2021CVE publishedPublication date reported by the CVE source.
  2. Nov 7, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=n/a

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

ClamAV · Cisco Secure Web Applianceversion=n/a

Published CVSS scores

7.4Cisco Systems, Inc.CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N/E:X/RL:X/RC:X
5.8NIST National Vulnerability DatabaseAV:N/AC:M/Au:N/C:P/I:P/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-296Improper Following of a Certificate's Chain of Trust
CWE-295Improper Certificate Validation
T1557Adversary-in-the-Middle

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo