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Email Security ApplianceApplication · Cisco

CVE-2021-1566

HIGH · 7.4 CVSS v3.1 Published 2021-06-16
Fix available
A fix is available. Upgrade to 11.8.3-021 / 12.0.3-005 or later.
See remediation →
83/100
Remediation priority · High
Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · moderate confidence

Improper TLS certificate validation in Cisco ESA and WSA devices when connecting to AMP servers allows a remote, unauthenticated attacker to perform man-in-the-middle attacks, potentially intercepting sensitive information or altering API requests between the affected device and AMP infrastructure.

MitigationApply the appropriate Cisco firmware update for ESA/WSA that addresses proper certificate validation, or ensure TLS certificate verification is properly configured in the AMP integration settings.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Email Security ApplianceApplication
Affected:all versions
AsyncosOperating system
Affected:< 12.5.3-035>= 13.0, < 13.0.0-030>= 13.5, < 13.5.3-010< 11.8.3-021>= 12.0.0, < 12.0.3-005>= 12.5.0, < 12.5.1-043
Web Security ApplianceApplication
Affected:all versions

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
High
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
None

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify the device model
    Check whether the device is a Cisco Email Security Appliance (ESA) or Cisco Web Security Appliance (WSA). This can be done via the admin web interface under System Administration > Product Identification, or via CLI command 'show version'.
    Affected if If the device is an ESA or WSA, proceed to next checks.
  2. Determine the installed firmware version
    For ESA: check via the web interface under Help and Tutorials > About or CLI command 'show version'. For WSA (AsyncOS): use CLI command 'show version' or web interface under System Administration > Software Upgrade. Compare the version number to the affected ranges: AsyncOS < 12.5.3-035; >= 13.0.0, < 13.0.0-030; >= 13.5.0, < 13.5.3-010; < 11.8.3-021; >= 12.0.0, < 12.0.3-005; >= 12.5.0, < 12.5.1-043. For ESA, all versions are affected.
    Affected if If the firmware version falls within any of the affected ranges, or if the device is ESA with any version, the vulnerability is potentially present.
  3. Verify AMP feature is enabled
    Check if Advanced Malware Protection (AMP) is configured on the device. For ESA: go to Security Services > IronPort Email Encryption (or AMP in newer versions) in the web interface, or use CLI command 'ampconfig'. For WSA: navigate to Security Services > Advanced Malware Protection in the web interface, or use CLI command 'amp'.
    Affected if If AMP is not enabled or configured, the vulnerability may not be exploitable as the device is not connecting to AMP servers.
  4. Inspect TLS certificate verification settings for AMP
    Review the AMP integration configuration to determine if TLS certificate validation is properly enforced. For ESA: check under the AMP or encryption settings in the web interface. For WSA: check under Security Services > Advanced Malware Protection > AMP Configuration. Look for settings related to TLS/SSL certificate verification or certificate validation for AMP cloud connections.
    Affected if If TLS certificate verification is disabled, set to permissive, or not explicitly enabled in the AMP configuration, the device is vulnerable to man-in-the-middle attacks.

The environment is affected if the device is a Cisco ESA (any version) or WSA with an affected AsyncOS version, and AMP is enabled with TLS certificate verification disabled or improperly configured.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

From vendor data
Upgrade available Upgrade to 11.8.3-021 / 12.0.3-005 / 12.5.1-043 or later
Fixed in 11.8.3-02112.0.3-00512.5.1-043
Interim mitigation

Apply the appropriate Cisco firmware update for ESA/WSA that addresses proper certificate validation, or ensure TLS certificate verification is properly configured in the AMP integration settings.

Fix this in Email Security Appliance Scoped from the published advisory
  • Consultation4.0 h
  • Implementation4.0 h
  • Testing2.0 h
  • Review / QA2.0 h
12.0 hours of engineering $2,180
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Scan for this in your stack

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2021-1566 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data