Security readout for executives and security teams
Plain-English summary
Cisco ESA could let an unauthenticated sender bypass configured attachment content filters by manipulating an attachment name. This does not indicate system takeover, but it can let attachments through controls intended to block them, weakening email security at the gateway.
Executive priority
Treat as a moderate email security control weakness. Prioritize if ESA is internet-facing mail infrastructure or attachment filtering is a primary malware prevention layer. It is less urgent than exploited remote code execution, but should not remain untracked.
Technical view
The flaw is CWE-20 improper input validation in Cisco AsyncOS attachment scanning for ESA. A specially patterned attachment name can bypass configured content filters. CVSS 3.0 is 5.8, network exploitable, no privileges, no user interaction, with limited integrity impact.
Likely exposure
Exposure is limited to organizations using Cisco Email Security Appliance running the affected AsyncOS version listed in the bundle: 12.0.0-419. Environments relying on ESA content filters for attachment blocking have the most relevant business risk.
Exploitation context
The provided bundle does not show CISA KEV listing or cite active exploitation. The vulnerability is remotely reachable by email and does not require authentication, but the documented impact is filter bypass, not direct code execution or device compromise.
Researcher notes
Evidence supports an unauthenticated remote content-filter bypass caused by improper input validation. The bundle names one affected version and does not provide exploit details, broad version ranges, or confirmed exploitation. Avoid extrapolating to other Cisco mail products without vendor evidence.
Mitigation direction
- Inventory Cisco ESA appliances and identify AsyncOS 12.0.0-419 deployments.
- Review Cisco's advisory for fixed releases or workarounds before changing production controls.
- Apply vendor-supported remediation according to Cisco guidance and maintenance windows.
- Monitor mail gateway events for unexpected attachment delivery past configured filters.
Validation and detection
- Confirm ESA model and AsyncOS version against the affected version in the advisory.
- Review content filter policy logs for attachment allow/block mismatches.
- After remediation, verify expected blocking with approved benign validation cases.
- Check vulnerability management records for closure evidence and Cisco advisory mapping.
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-20: 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-2019-1921 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
- Medium
- CVSS
- 5.8 (3.0)
- Known Exploited
- No
- Published
Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/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:3.0/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N3.91.4Primary CVE scoreVulnerability scoring details
Base CVSS 3.0 score
5.8MediumVector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N
Source materials
- CVE List V5 sourceCVE List V5
- 20190703 Cisco Email Security Appliance Content Filter Bypass 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 Input Validation
Improper Input Validation represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.