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Email Security ApplianceApplication · Cisco

CVE-2015-6291

HIGH · 7.8 CVSS v2.0 Published 2015-11-06
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
87/100
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
Cisco AsyncOS before 8.5.7-043, 9.x before 9.1.1-023, and 9.5.x and 9.6.x before 9.6.0-046 on Email Security Appliance (ESA) devices mishandles malformed fields during body-contains, attachment-contains, every-attachment-contains, attachment-binary-contains, dictionary-match, and attachment-dictionary-match filtering, which allows remote attackers to cause a denial of service (memory consumption) via a crafted attachment in an e-mail message, aka Bug ID CSCuv47151.

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

Cisco Email Security Appliance (ESA) devices running affected AsyncOS versions contain a denial of service vulnerability in content filtering logic. When processing malformed fields during attachment-based filtering operations (body-contains, attachment-contains, every-attachment-contains, attachment-binary-contains, dictionary-match, and attachment-dictionary-match), the device can be forced into excessive memory consumption by a crafted email attachment, potentially rendering the device unresponsive.

MitigationUpgrade Cisco AsyncOS to version 8.5.7-043, 9.1.1-023, or 9.6.0-046 or later as appropriate for the deployed release train. Apply during a scheduled maintenance window with full functionality testing post-upgrade.

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:= 7.7.0-000= 7.7.1-000= 8.0_base= 8.5.6-052= 8.5.6-073= 8.5.6-074= 8.5.6-106= 8.5.6-113= 8.5.7-042= 8.5_base= 9.0.0= 9.0.0-212

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
Authentication
None
Confidentiality
None
Integrity
None
Availability
Complete

AV:N/AC:L/Au:N/C:N/I:N/A:C

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 installed AsyncOS version
    Log into the ESA CLI and run the 'version' command, or access the web interface and navigate to System Administration > Software Updates to view the current AsyncOS version.
    Affected if The version number matches any of the following: 7.7.0-000, 7.7.1-000, 8.0_base, 8.5.6-052, 8.5.6-073, 8.5.6-074, 8.5.6-106, 8.5.6-113, 8.5.7-042, 8.5_base, 9.0.0, or 9.0.0-212.
  2. Confirm content filtering is enabled
    Access the ESA web interface and navigate to Mail Policies > Incoming Content Filters or Outgoing Content Filters, or use the CLI command 'filterconfig' to view filter settings.
    Affected if Content filtering is enabled and configured for incoming or outgoing mail policies.
  3. Review filter configurations for vulnerable filter types
    In the content filter settings, examine each active filter to identify if any use the following filter types: body-contains, attachment-contains, every-attachment-contains, attachment-binary-contains, dictionary-match, or attachment-dictionary-match.
    Affected if Any content filter is configured using one or more of the following filter types: body-contains, attachment-contains, every-attachment-contains, attachment-binary-contains, dictionary-match, or attachment-dictionary-match.

A user is affected if their ESA runs an affected AsyncOS version AND has content filtering enabled with any of the vulnerable filter types (body-contains, attachment-contains, every-attachment-contains, attachment-binary-contains, dictionary-match, or attachment-dictionary-match) configured.

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 version 8.5.7-043, 9.1.1-023, or 9.6.0-046 or later as appropriate for the deployed release train. Apply during a scheduled maintenance window with full functionality testing post-upgrade.

Fix this in Email Security Appliance Scoped from the published advisory
  • Consultation4.0 h
  • Implementation4.0 h
  • Testing6.0 h
  • Review / QA2.0 h
16.0 hours of engineering $2,780
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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-2015-6291 in production — separate from our analysis above.

No notes yet

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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