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Email Security ApplianceApplication · Cisco

CVE-2016-6372

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 and content filtering for malformed Multipurpose Internet Mail Extensions (MIME) headers of Cisco AsyncOS Software for Cisco Email Security Appliances (ESA) and Web Security Appliances (WSA) could allow an unauthenticated, remote attacker to bypass the filtering functionality of the targeted device. Emails that should have been quarantined could instead be processed. Affected Products: This vulnerability affects all releases prior to the first fixed release of Cisco AsyncOS Software for Cisco ESA and Cisco WSA on both virtual and hardware appliances that are configured with message or content filters to scan incoming email attachments. More Information: CSCuy54740, CSCuy75174. Known Affected Releases: 9.7.1-066 9.5.0-575 WSA10.0.0-000. 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 Cisco AsyncOS email and content filtering allows malformed MIME headers to bypass quarantine rules. An unauthenticated remote attacker can craft emails with specially malformed MIME headers that evade filtering and get processed instead of being quarantined on affected ESA and WSA appliances.

MitigationUpgrade Cisco AsyncOS Software to the fixed releases (10.0.0-125, 9.1.1-038, or 9.7.2-047) on both ESA and WSA appliances, prioritizing those with message or content filters enabled for incoming email scanning.

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:= 8.0.1-023= 8.0_base= 8.5.0-000= 8.5.0-er1-198= 8.5.6-052= 8.5.6-073= 8.5.6-074= 8.5.6-106= 8.5.6-113= 8.5.7-042= 8.6.0= 8.6.0-011
Web Security ApplianceApplication
Affected:= 5.6.0-623= 6.0.0-000= 7.1.0= 7.1.1= 7.1.2= 7.1.3= 7.1.4= 7.5.0-000= 7.5.0-825= 7.5.1-000= 7.5.2-000= 7.5.2-hp2-303
Web Security Appliance 8.0.5Application
Affected:= hot_patch_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
High
Integrity
None
Availability
None

CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/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. Identify the Cisco appliance type
    Log into the device CLI and run the 'version' command, or check the web interface header to determine if the device is an Email Security Appliance (ESA) or Web Security Appliance (WSA)
    Affected if The device is a Cisco ESA or WSA appliance running AsyncOS software
  2. Check AsyncOS version on Email Security Appliance
    In the ESA CLI, run 'version' or use the web interface under System Administration > Software Updates. Compare the displayed version string against the affected ESA versions: 8.0.1-023, 8.0_base, 8.5.0-000, 8.5.0-er1-198, 8.5.6-052, 8.5.6-073, 8.5.6-074, 8.5.6-106, 8.5.6-113, 8.5.7-042, 8.6.0, 8.6.0-011
    Affected if The installed ESA AsyncOS version exactly matches one of the listed vulnerable versions
  3. Check AsyncOS version on Web Security Appliance
    In the WSA CLI, run 'version' or use the web interface under System Administration > Software Updates. Compare the displayed version string against the affected WSA versions: 5.6.0-623, 6.0.0-000, 7.1.0, 7.1.1, 7.1.2, 7.1.3, 7.1.4, 7.5.0-000, 7.5.0-825, 7.5.1-000, 7.5.2-000, 7.5.2-hp2-303, and hot_patch_1 for version 8.0.5
    Affected if The installed WSA AsyncOS version exactly matches one of the listed vulnerable versions
  4. Verify message or content filters are enabled
    On ESA, go to Mail Policies > Incoming Mail Policies in the web interface or run 'filters' in the CLI. On WSA, check Security Services > Content Filters. Confirm that filters are actively configured for incoming email scanning
    Affected if Message filters or content filters are enabled and configured to scan incoming email

The environment is affected if either an ESA or WSA is running one of the specific vulnerable AsyncOS versions listed and has message or content filters enabled for incoming email scanning.

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 to the fixed releases (10.0.0-125, 9.1.1-038, or 9.7.2-047) on both ESA and WSA appliances, prioritizing those with message or content filters enabled for incoming email scanning.

Fix this in Email Security Appliance Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing4.0 h
  • Review / QA2.0 h
12.0 hours of engineering $2,080
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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-2016-6372 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
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data