CVE-2021-1566

Cisco Email Security Appliance and Cisco Web Security Appliance Certificate Validation Vulnerability

HIGH

7.4

CVSS Score

Published: June 16, 2021 at 05:45 PM UTC

Updated: June 17, 2026 at 03:32 AM UTC

3 products affected across 1 vendorEmail Security ApplianceWeb Security ApplianceAsyncos

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Severity

HIGH7.4

Exploit prediction

EPSS 0.7%

SSVC

No known exploit

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.

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

Asyncos · Cisco

95%

v < 11.8.3-021v < 12.5.3-03512.0.0 ≤ v < 12.0.3-00512.5.0 ≤ v < 12.5.1-04313.0 ≤ v < 13.0.0-03013.5 ≤ v < 13.5.3-010

Affected range stops below 11.8.3-021, so it looks safe — our inference, not a vendor statement

Affected range stops below 12.0.3-005, so it looks safe — our inference, not a vendor statement

Affected range stops below 12.5.1-043, so it looks safe — our inference, not a vendor statement

Affected range stops below 12.5.3-035, so it looks safe — our inference, not a vendor statement

Affected range stops below 13.0.0-030, so it looks safe — our inference, not a vendor statement

Affected range stops below 13.5.3-010, so it looks safe — our inference, not a vendor statement

Email Security Appliance · Cisco

95%

All versions

Web Security Appliance · Cisco

95%

All versions

Remediation

No guide yet

No remediation guidance has been written for this CVE yet. What the record does show:

Patch and advisory references

https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-esa-wsa-cert-vali-n8L97RW

References (1)

Vendor Advisoryx_refsource_CISCO

Source: [email protected]

https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-esa-wsa-cert-vali-n8L97RW

SSVC — Action Prioritization

SSVCNo known exploitNot automatableTotal impact

SSVC signals action urgency (what to patch first), separate from CVSS which measures severity.

CVSS

7.4HIGHcisco

Attack Vector: NETWORK
Complexity: HIGH
Privileges: NONE
User Interaction: NONE
Scope: UNCHANGED
Confidentiality: HIGH
Integrity: HIGH
Availability: NONE

Vector?

Quick Info

StatusMODIFIED

CWE

CWE-296CWE-295

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