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Email Security Appliance FirmwareOperating system · Cisco

CVE-2017-3818

MEDIUM · 5.8 CVSS v3.0 Published 2017-02-03
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
67/100
Remediation priority · Elevated
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 Multipurpose Internet Mail Extensions (MIME) scanner of Cisco AsyncOS Software for Cisco Email Security Appliances (ESA) could allow an unauthenticated, remote attacker to bypass configured user filters on the device, aka a Malformed MIME Header Filtering Bypass. This vulnerability affects all releases prior to the first fixed release of Cisco AsyncOS Software for Cisco Email Security Appliances, both virtual and hardware appliances, if the software is configured to apply a message filter or content filter to incoming email attachments. More Information: CSCvb65245. Known Affected Releases: 9.7.1-066. Known Fixed Releases: 9.8.0-092.

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 · high confidence

A vulnerability in the MIME scanner of Cisco AsyncOS for Email Security Appliances allows unauthenticated remote attackers to bypass configured message and content filters by sending specially crafted (malformed) MIME headers in email attachments. The filter bypass occurs when the device processes incoming emails with malformed MIME headers that the scanner fails to properly inspect.

MitigationUpgrade Cisco AsyncOS Software for ESA to version 9.8.0-092 or later. Until upgraded, consider implementing additional layered filtering or manual inspection for suspicious attachments.

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 Appliance FirmwareOperating system
Affected:= 9.7.1-066

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
Low
Privileges
None
User interaction
None
Scope
Changed
Confidentiality
None
Integrity
Low
Availability
None

CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/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. Determine the installed AsyncOS version
    Access the ESA CLI and run the 'version' command, or log into the web interface and navigate to System Administration > Software Version to view the currently installed Cisco AsyncOS for Email Security Appliance firmware version.
    Affected if The installed version is exactly 9.7.1-066 (the only affected version listed)
  2. Confirm the version string matches exactly
    Review the full version output. Note that the vulnerability applies specifically to version 9.7.1-066 as listed in the affected products. Compare your displayed version number against this exact value.
    Affected if The version displayed is 9.7.1-066 (not a later patched version such as 9.8.0-092 or newer)
  3. Verify message or content filters are configured
    In the ESA web interface, navigate to Mail Policies > Message Filters or Content Filters to confirm filters are actively defined. In the CLI, use 'filters' or 'list filters' command to display configured filters.
    Affected if Message or content filters are actively configured and would process incoming email attachments
  4. Confirm the MIME scanner is active for incoming mail
    In the ESA web interface, check under Mail Policies > Inbound Mail Policies or Scanning Settings to verify that MIME/attachment scanning is enabled. In the CLI, use 'scanconfig' or 'mimescan' to check scanner status.
    Affected if MIME/attachment scanning is enabled and processing incoming emails through the device

You are affected if your ESA runs exactly version 9.7.1-066 and has MIME scanning and message/content filters enabled for incoming email.

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
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Upgrade Cisco AsyncOS Software for ESA to version 9.8.0-092 or later. Until upgraded, consider implementing additional layered filtering or manual inspection for suspicious attachments.

Fix this in Email Security Appliance Firmware Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing6.0 h
  • Review / QA2.0 h
20.0 hours of engineering $3,500
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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-2017-3818 in production — separate from our analysis above.

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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
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  • Version or environment caveats, and links to real fixes
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