Security readout for executives and security teams
Plain-English summary
This flaw affects Cisco Email Security Appliance email filtering. A remote attacker could make certain SPF-related input bypass configured header filters, allowing malicious email content to pass controls that administrators expected to block it.
Executive priority
Treat this as a moderate email security control-bypass issue. Prioritize organizations relying on Cisco ESA header filters to block malicious or policy-violating mail, especially internet-facing mail gateways.
Technical view
CVE-2019-1955 is an input validation issue in Cisco AsyncOS SPF handling for Cisco ESA. The CVSS 3.0 score is 5.3. It is remotely reachable, requires no authentication or user interaction, and can bypass configured header filters, creating limited integrity impact.
Likely exposure
Exposure is most likely where Cisco ESA processes inbound email with SPF functionality and configured header or user filters. The source bundle does not identify affected AsyncOS versions, CPEs, or deployment prerequisites beyond Cisco ESA.
Exploitation context
The CVE record describes unauthenticated remote exploitation using crafted SPF-related input. The provided sources do not show CISA KEV listing or active exploitation evidence, so active exploitation should not be assumed.
Researcher notes
The evidence supports CWE-20 input validation weakness, network attack vector, low attack complexity, and limited integrity impact. Affected versions are unspecified in the provided bundle, so version-level exposure must come from Cisco’s advisory.
Mitigation direction
- Review Cisco’s advisory for affected AsyncOS ESA releases and official fixes.
- Apply Cisco-recommended software updates or configuration guidance where applicable.
- Verify header filters enforce intended policy after remediation.
- Increase monitoring for email content bypassing expected gateway controls.
- Use upstream or downstream mail filtering as temporary compensating control.
Validation and detection
- Inventory Cisco ESA deployments and AsyncOS versions.
- Confirm whether SPF functionality and header filters are enabled.
- Compare deployments against Cisco’s affected and fixed release guidance.
- Review mail gateway logs for unexpected filter bypass behavior.
- Validate filter behavior in a controlled environment using vendor-approved checks.
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
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CWE-20: Exact CWE lookup
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Open ATT&CK lookupCVE-2019-1955 mapping review
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Open ATT&CK lookup- Severity
- Medium
- CVSS
- 5.3 (3.0)
- Known Exploited
- No
- Published
Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/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:U/C:N/I:L/A:N3.91.4Primary CVE scoreVulnerability scoring details
Base CVSS 3.0 score
5.3MediumVector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
Source materials
- CVE List V5 sourceCVE List V5
- 20190807 Cisco Email Security Appliance Header Injection 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.