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Web Security ApplianceApplication · Cisco

CVE-2015-6386

MEDIUM · 5.0 CVSS v2.0 Published 2015-12-01
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
59/100
Remediation priority · Elevated
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
The passthrough FTP feature on Cisco Web Security Appliance (WSA) devices with software 8.0.7-142 and 8.5.1-021 allows remote attackers to cause a denial of service (CPU consumption) via FTP sessions in which the control connection is ended after data transfer, aka Bug ID CSCut94150.

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

The Cisco Web Security Appliance contains a denial of service vulnerability in the passthrough FTP feature. When FTP sessions end with the control connection closing after data transfer completes (rather than proper session termination), the device enters a CPU consumption loop. This affects versions 8.0.7-142 and 8.5.1-021, causing the WSA to become unresponsive due to resource exhaustion.

MitigationUpgrade Cisco WSA software to a patched version beyond 8.0.7-142 and 8.5.1-021. As a workaround, consider disabling the passthrough FTP feature or implementing network-level rate limiting on FTP traffic until the upgrade can be applied.

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:= 8.0.7-142= 8.5.1-021

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
Partial

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

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 WSA device and version
    Access the Cisco WSA CLI and run the 'version' command, or check the version via the web interface under System Administration > System Upgrade. Record the exact software version string.
    Affected if The installed version is exactly 8.0.7-142 or exactly 8.5.1-021.
  2. Verify passthrough FTP feature is enabled
    Log into the WSA web interface and navigate to the FTP proxy settings (Security Services > FTP). Confirm the FTP Proxy / Passthrough FTP option is turned ON. In CLI, this may be visible via 'ftpconfig' or 'proxysettings' commands.
    Affected if Passthrough FTP is enabled on the appliance.
  3. Check for high CPU utilization
    In the WSA CLI, run the command 'status' or 'top' to view CPU usage. Look for abnormally high CPU consumption, particularly by FTP-related processes. In the web interface, monitor the Dashboard for sustained high CPU warnings.
    Affected if CPU utilization is excessively high and remains elevated, especially if FTP traffic is passing through.
  4. Monitor for FTP-related process loops
    Use the 'grep FTP /var/log/.*' command in WSA CLI to search logs for unusual FTP session patterns. Check if FTP data transfers complete but sessions remain in a hanging state, indicated by incomplete session closure messages in the proxy logs.
    Affected if Logs show FTP sessions ending with control connection closing after data transfer but without proper session termination.

A user is affected if the WSA runs exactly version 8.0.7-142 or 8.5.1-021, has passthrough FTP enabled, and exhibits high CPU or hung FTP sessions when FTP traffic passes through the appliance.

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 WSA software to a patched version beyond 8.0.7-142 and 8.5.1-021. As a workaround, consider disabling the passthrough FTP feature or implementing network-level rate limiting on FTP traffic until the upgrade can be applied.

Fix this in Web Security Appliance Scoped from the published advisory
  • Consultation4.0 h
  • Implementation2.0 h
  • Testing6.0 h
  • Review / QA2.0 h
14.0 hours of engineering $2,420
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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-2015-6386 in production — separate from our analysis above.

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What this is

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What belongs here
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  • Version or environment caveats, and links to real fixes
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