dbcve.org
Web Security ApplianceApplication · Cisco

CVE-2015-6321

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 8.5.7-042, 9.x before 9.1.0-032, 9.1.x before 9.1.1-023, and 9.5.x and 9.6.x before 9.6.0-042 on Email Security Appliance (ESA) devices; before 9.1.0-032, 9.1.1 before 9.1.1-005, and 9.5.x before 9.5.0-025 on Content Security Management Appliance (SMA) devices; and before 7.7.0-725 and 8.x before 8.0.8-113 on Web Security Appliance (WSA) devices allows remote attackers to cause a denial of service (memory consumption) via a flood of TCP packets, aka Bug IDs CSCus79774, CSCus79777, and CSCzv95795.

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 AsyncOS on Email Security Appliance (ESA), Content Security Management Appliance (SMA), and Web Security Appliance (WSA) devices contains a memory consumption vulnerability where remote attackers can cause denial of service by flooding TCP packets, leading to memory exhaustion and service unavailability.

MitigationUpgrade Cisco AsyncOS to version 8.5.7-042, 9.1.0-032, 9.1.1-023, 9.6.0-042 or later for ESA; 9.1.0-032, 9.1.1-005, 9.5.0-025 or later for SMA; and 7.7.0-725, 8.0.8-113 or later for WSA. As interim mitigation, implement network-level rate limiting or firewall filters to reduce TCP flood impact.

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
Web Security ApplianceApplication
Affected:= 5.6.0-623= 6.0.0-000= 7.5.0-000= 7.5.0-825= 7.5.1-000= 7.5.2-000= 7.7.0-000= 7.7.1-000= 8.0.0-000= 8.5.0.000
Content Security Management ApplianceApplication
Affected:= 7.8.0-328= 7.8.1-001= 7.9.0-201= 7.9.2-116= 8.0.1-031= 8.1.0-001= 8.1.1-033= 8.1.2-000= 8.2.0-238= 8.3.0-350= 8.3.5-061= 8.3.6-014
Email Security ApplianceApplication
Affected:= 7.6.1-000= 7.6.3-000= 7.7.0-000= 7.7.1-000= 7.8.0-311= 8.5.6-052= 8.6.0-011= 8.9.1-000= 8.9.2-032= 9.0.0-212= 9.0.5-000= 9.1.0-011

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 the Cisco appliance type
    Access the device CLI or web interface and confirm whether the device is an Email Security Appliance (ESA), Content Security Management Appliance (SMA), or Web Security Appliance (WSA). In CLI, run 'estap' or check the system overview in the web GUI.
    Affected if The device is any of these three appliance types (ESA, SMA, or WSA) running the affected AsyncOS versions.
  2. Retrieve the AsyncOS version
    In the device CLI, run the command 'version' or 'show version' to display the installed AsyncOS version and build number.
    Affected if The displayed version and build number matches one of the listed affected versions for the appliance type.
  3. Confirm WSA version matches affected list
    If the device is a WSA, compare the version output against: 5.6.0-623, 6.0.0-000, 7.5.0-000, 7.5.0-825, 7.5.1-000, 7.5.2-000, 7.7.0-000, 7.7.1-000, 8.0.0-000, or 8.5.0.000
    Affected if The installed WSA version exactly matches one of these build numbers.
  4. Confirm SMA version matches affected list
    If the device is an SMA, compare the version output against: 7.8.0-328, 7.8.1-001, 7.9.0-201, 7.9.2-116, 8.0.1-031, 8.1.0-001, 8.1.1-033, 8.1.2-000, 8.2.0-238, 8.3.0-350, 8.3.5-061, or 8.3.6-014
    Affected if The installed SMA version exactly matches one of these build numbers.
  5. Confirm ESA version matches affected list
    If the device is an ESA, compare the version output against: 7.6.1-000, 7.6.3-000, 7.7.0-000, 7.7.1-000, 7.8.0-311, 8.5.6-052, 8.6.0-011, 8.9.1-000, 8.9.2-032, 9.0.0-212, 9.0.5-000, or 9.1.0-011
    Affected if The installed ESA version exactly matches one of these build numbers.
  6. Verify network exposure to untrusted TCP traffic
    Review the device network configuration to determine if the ESA, SMA, or WSA is directly accessible from untrusted networks or the internet on any TCP port.
    Affected if The appliance accepts TCP connections from untrusted networks, making it susceptible to the TCP flood attack that triggers memory exhaustion.

If the device is an ESA, SMA, or WSA and its AsyncOS version matches exactly one of the specific build numbers listed for that appliance type AND it accepts TCP traffic from untrusted networks, the environment is affected by this vulnerability.

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 8.5.7-042, 9.1.0-032, 9.1.1-023, 9.6.0-042 or later for ESA; 9.1.0-032, 9.1.1-005, 9.5.0-025 or later for SMA; and 7.7.0-725, 8.0.8-113 or later for WSA. As interim mitigation, implement network-level rate limiting or firewall filters to reduce TCP flood impact.

Fix this in Web Security Appliance Scoped from the published advisory
  • Consultation3.0 h
  • Implementation4.0 h
  • Testing2.0 h
  • Review / QA1.0 h
10.0 hours of engineering $1,800
Get help mitigating

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,880.

Scan for this in your stack

Free · runs locally
dbcve dependency scanner

Check whether your project pulls in CVE-2015-6321 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.

Get it on GitHub Scan in the browser

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-2015-6321 in production — separate from our analysis above.

No notes yet

Be the first to add a field note for this CVE — a mitigation you’ve verified, a version caveat, or a link to a working fix. Sign in above to contribute.

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