Security readout for executives and security teams
Plain-English summary
This flaw affects Cisco security appliances when their AMP integration connects to Cisco AMP servers. Because TLS certificate validation is improper, an attacker positioned between the appliance and AMP servers could impersonate a trusted host, read sensitive traffic, or alter some API requests. Business impact is mainly confidentiality and integrity risk for email or web security operations.
Executive priority
Prioritize remediation as a high-risk network trust issue, especially where ESA or WSA appliances protect sensitive mail or web traffic. There is no cited active exploitation, but the potential to read or alter security-service traffic justifies timely vendor-guided patching and validation.
Technical view
CVE-2021-1566 is CWE-296 in Cisco AsyncOS AMP for Endpoints integration for Cisco ESA and WSA. It allows an unauthenticated remote man-in-the-middle attacker to exploit improper certificate validation during TLS establishment. CVSS 3.1 is 7.4, with network attack vector, high complexity, no privileges, no user interaction, and high confidentiality and integrity impact.
Likely exposure
Exposure is likely limited to organizations running affected Cisco ESA or WSA appliances with AMP for Endpoints integration enabled. The provided bundle does not list exact affected versions. The attacker must be able to intercept traffic between the appliance and AMP servers, so network position matters.
Exploitation context
The source bundle does not show CISA KEV listing or other evidence of active exploitation. Exploitation requires a man-in-the-middle position and crafted TLS interaction, reflected by CVSS high attack complexity. Treat as serious because successful exploitation can expose sensitive data or alter API requests.
Researcher notes
The bundle names Cisco WSA in the affected list, while the title and description cover ESA and WSA. Exact affected versions and fixed releases are not included in the provided data, so validation should rely on Cisco's advisory rather than assumptions.
Mitigation direction
- Review Cisco advisory for affected releases, fixed versions, and any vendor workarounds.
- Inventory Cisco ESA and WSA appliances using AMP for Endpoints integration.
- Prioritize remediation for appliances on untrusted, shared, or poorly monitored network paths.
- Monitor appliance-to-AMP communications for TLS anomalies, unexpected destinations, or API irregularities.
- Document the remediation decision and maintenance window for security leadership.
Validation and detection
- Confirm whether Cisco ESA or WSA appliances are deployed in the environment.
- Check whether AMP for Endpoints integration is enabled on each appliance.
- Compare appliance AsyncOS versions against Cisco advisory guidance.
- Review network telemetry for unusual appliance-to-AMP TLS connection patterns.
- Verify remediation state after vendor-recommended updates or configuration changes.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-296: Exact CWE lookup
Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupCVE-2021-1566 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- High
- CVSS
- 7.4 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N2.25.2Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
7.4HighVector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
Source materials
- CVE List V5 sourceCVE List V5
- 20210616 Cisco Email Security Appliance and Cisco Web Security Appliance Certificate Validation VulnerabilityCVE reference · vendor-advisory, x_refsource_CISCO
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Improper Following of a Certificate's Chain of Trust
Improper Following of a Certificate's Chain of Trust represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.