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Email Security ApplianceApplication · Cisco

CVE-2016-6356

HIGH · 7.5 CVSS v3.0 Published 2016-10-28
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
84/100
Remediation priority · High
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 email message filtering feature of Cisco AsyncOS Software for Cisco Email Security Appliances could allow an unauthenticated, remote attacker to cause an affected device to stop scanning and forwarding email messages due to a denial of service (DoS) condition. Affected Products: 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. The vulnerability is not limited to any specific rules or actions for a message filter or content filter. More Information: CSCuz63143. Known Affected Releases: 8.5.7-042 9.7.0-125. Known Fixed Releases: 10.0.0-125 9.1.1-038 9.7.2-047.

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 email message filtering feature of Cisco AsyncOS for Email Security Appliances allows an unauthenticated remote attacker to cause a DoS condition. When the device is configured to apply message or content filters to incoming email attachments, specially crafted attachments can cause the device to stop scanning and forwarding email messages.

MitigationUpgrade Cisco AsyncOS to a fixed release (10.0.0-125, 9.1.1-038, or 9.7.2-047). If immediate upgrade is not possible, consider disabling attachment filtering or implementing additional email gateway protections to mitigate the risk.

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 ApplianceApplication
Affected:= 3.3.1-09= 7.1.0= 7.1.1= 7.1.2= 7.1.3= 7.1.4= 7.1.5= 7.3.0= 7.3.1= 7.3.2= 7.5.0= 7.5.1

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
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

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. Check the Cisco AsyncOS version
    Log into the Email Security Appliance CLI and run the 'version' command, or access the web interface and navigate to System Administration > AsyncOS Upgrade to view the current version
    Affected if The displayed version matches one of these: 3.3.1-09, 7.1.0, 7.1.1, 7.1.2, 7.1.3, 7.1.4, 7.1.5, 7.3.0, 7.3.1, 7.3.2, 7.5.0, or 7.5.1
  2. Verify if message filters are configured
    Access the web interface and navigate to Mail Policies > Message Filters, or run 'filters' command in the CLI to list active filters
    Affected if Any message filter rules reference the 'attachment' filter type or attachment-related conditions
  3. Verify if content filters are configured
    Access the web interface and navigate to Mail Policies > Content Filters, or run 'contentfilters' in the CLI to list active content filters
    Affected if Any content filter rules are enabled and configured to act on email attachments
  4. Confirm attachment scanning is active
    Check the incoming mail flow configuration in the web interface under Mail Policies > Incoming Mail Policies to see if filters that process attachments are applied to any mail flow
    Affected if Incoming mail policies have filters enabled that process attachments from external sources

You are affected if your Cisco Email Security Appliance runs an affected version (3.3.1-09, 7.1.x through 7.5.1) AND has message or content filters configured to act on incoming email attachments.

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 to a fixed release (10.0.0-125, 9.1.1-038, or 9.7.2-047). If immediate upgrade is not possible, consider disabling attachment filtering or implementing additional email gateway protections to mitigate the risk.

Fix this in Email Security Appliance Scoped from the published advisory
  • Consultation3.0 h
  • Implementation6.0 h
  • Testing3.0 h
  • Review / QA2.0 h
14.0 hours of engineering $2,490
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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-2016-6356 in production — separate from our analysis above.

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What this is

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What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
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