CVE-2017-3818 Cisco CVE debrief

Who should care

Email security and messaging teams running Cisco ESA, especially environments that apply message filters or content filters to incoming email attachments. Internet-facing mail gateways and defenders relying on ESA to block or inspect attachments should prioritize review.

Technical summary

According to the CVE and NVD record, the weakness is a MIME scanner filtering bypass in Cisco AsyncOS for ESA. The affected configuration is when the appliance is set to apply a message filter or content filter to incoming email attachments. NVD maps the issue to CWE-20 and assigns CVSS 3.0 vector CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N, indicating network attackability with no privileges or user interaction required and a limited integrity impact.

Defensive priority

Medium. The flaw is remotely reachable and can undermine attachment filtering on mail security appliances, but the published impact is limited to integrity with no confidentiality or availability impact in the NVD vector.

Recommended defensive actions

• Upgrade Cisco AsyncOS Software for Cisco Email Security Appliances to the first fixed release or later; the source corpus lists 9.8.0-092 as the known fixed release.
• Verify whether the ESA is configured to apply message filters or content filters to incoming email attachments, since that is the affected condition described by Cisco.
• Use the Cisco security advisory and NVD entry to confirm affected versions and any vendor-provided mitigation guidance.
• Check asset inventories for ESA appliances running affected pre-fix releases, including both virtual and hardware deployments.
• Review mail security logs and policy outcomes for unexpected attachment-filter bypass behavior until remediation is complete.

Evidence notes

CVE published on 2017-02-03 and later modified in NVD on 2026-05-13; those timestamps are taken from the supplied CVE and source timeline and should not be treated as the issue creation time. The source corpus identifies Cisco AsyncOS Software for Cisco ESA as the affected product, describes a malformed MIME header filtering bypass, and lists known affected release 9.7.1-066 and known fixed release 9.8.0-092. NVD references Cisco's vendor advisory and classifies the weakness as CWE-20 with CVSS 5.8 Medium.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.