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Web Security ApplianceApplication · Cisco

CVE-2016-6407

HIGH · 7.5 CVSS v3.0 Published 2016-09-17
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
Cisco AsyncOS through 9.5.0-444 on Web Security Appliance (WSA) devices allows remote attackers to cause a denial of service (link saturation) by making many HTTP requests for overlapping byte ranges simultaneously, aka Bug ID CSCuz27219.

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 · moderate confidence

Cisco AsyncOS before 9.5.0-444 on Web Security Appliance (WSA) devices contains a denial of service vulnerability where remote attackers can saturate network links by sending many simultaneous HTTP requests with overlapping byte ranges (Range header abuse). This causes the WSA to consume excessive bandwidth processing these requests, making the device unavailable.

MitigationUpgrade Cisco AsyncOS to the patched version (consult Cisco advisory for exact version). Implement network-level rate limiting or HTTP request throttling at perimeter devices as a compensating control until firmware update can be completed.

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= 7.1.0= 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

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. Confirm device is a Cisco Web Security Appliance
    Check the device model number on the physical appliance label, or log into the WSA web interface and look at the Dashboard or System Administration > Network Configuration for the appliance model description.
    Affected if The device is not a Cisco WSA, this CVE does not apply.
  2. Identify the installed AsyncOS version
    Log into the WSA CLI (SSH or console) and run the command 'version', or via the web interface go to System Administration > Cisco AsyncOS Software Upgrade to view the current version. Note the full version string (e.g., 7.5.2-303).
    Affected if This step identifies the installed version to compare against the affected range.
  3. Compare installed version to affected range
    The affected (vulnerable) versions are: 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 any version before 9.5.0-444. Compare your installed version from step 2 to this list.
    Affected if The installed version matches one of the listed versions or is earlier than 9.5.0-444.
  4. Observe network bandwidth for abnormal patterns
    Monitor the WSA network interface throughput using SNMP, the WSA web interface (Monitor > Bandwidth), or external network monitoring tools. Look for unusually high bandwidth consumption from many simultaneous HTTP requests.
    Affected if You observe sustained high bandwidth from many overlapping HTTP Range header requests, which may indicate active exploitation of this vulnerability.

You are affected if your Cisco WSA is running any AsyncOS version that matches the affected versions listed or is earlier than 9.5.0-444.

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 the patched version (consult Cisco advisory for exact version). Implement network-level rate limiting or HTTP request throttling at perimeter devices as a compensating control until firmware update can be completed.

Fix this in Web Security Appliance Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing3.0 h
  • Review / QA2.0 h
11.0 hours of engineering $1,930
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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-2016-6407 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
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  • No spam, self-promotion, credentials, or personal data