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iOSOperating system · Cisco

CVE-2016-6380

HIGH · 8.1 CVSS v3.0 Published 2016-10-05
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
90/100
Remediation priority · Urgent
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 DNS forwarder in Cisco IOS 12.0 through 12.4 and 15.0 through 15.6 and IOS XE 3.1 through 3.15 allows remote attackers to obtain sensitive information from process memory or cause a denial of service (data corruption or device reload) via a crafted DNS response, aka Bug ID CSCup90532.

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 the DNS forwarder component of Cisco IOS 12.0-12.4 and 15.0-15.6, as well as IOS XE 3.1-3.15, allows remote attackers to send crafted DNS responses that can either leak sensitive information from process memory or cause denial of service through data corruption or device reload.

MitigationApply the relevant Cisco security update or upgrade to a patched IOS/IOS XE version. If patching is delayed, restrict DNS forwarding to trusted internal networks or disable the feature if unnecessary.

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
iOSOperating system
Affected:= 12.0\(3\)t= 12.0\(3\)t1= 12.0\(3\)t2= 12.0\(3\)t3= 12.0\(3\)xe= 12.0\(3\)xe1= 12.0\(3\)xe2= 12.0\(4\)t= 12.0\(4\)t1= 12.0\(4\)xe= 12.0\(4\)xe1= 12.0\(4\)xe2
Ios XeOperating system
Affected:= 3.1.0s= 3.1.0sg= 3.1.1s= 3.1.1sg= 3.1.2s= 3.1.3as= 3.1.4as= 3.1.4s= 3.2.0se= 3.2.1s= 3.2.1se= 3.2.2s
Ios Xe 3.2jaOperating system
Affected:= 3.2.0ja
Ios Xe 3.3sgOperating system
Affected:= 3.3.0sg= 3.3.1sg= 3.3.2sg
Ios Xe 3.3xoOperating system
Affected:= 3.3.0xo= 3.3.1xo= 3.3.2xo
Ios Xe 3.4sgOperating system
Affected:= 3.4.0sg= 3.4.1sg= 3.4.2sg= 3.4.3sg= 3.4.4sg= 3.4.5sg= 3.4.6sg= 3.4.7sg

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
High
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/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. Identify the IOS or IOS XE version
    Run 'show version' on the device CLI to obtain the exact software version string (e.g., 12.4(25e), 15.1(4)M, 3.1.0S)
    Affected if The displayed version matches any of the specific versions in the CVE or falls within the 12.0-12.4, 15.0-15.6 (IOS) or 3.1-3.15 (IOS XE) ranges listed in the affected products
  2. Confirm the DNS forwarder feature is enabled
    Run 'show ip dns forwarding' or check the configuration with 'show running-config | include dns' to see if DNS forwarding is configured
    Affected if DNS forwarding is enabled (the feature is active on the device)
  3. Verify DNS server configuration
    Run 'show ip dns primary' or 'show running-config | include ip name-server' to list configured DNS servers
    Affected if External DNS servers are configured and the device forwards DNS queries (the forwarder is operational)
  4. Check for recent DNS-related process crashes
    Run 'show log | include DNS' or 'show crashinfo' to look for DNS process errors or reloads
    Affected if There are recent DNS-related crashes or error messages in the logs indicating potential exploitation

The device is likely affected if it runs any IOS version in the 12.0-12.4 or 15.0-15.6 range, or any IOS XE version in the 3.1-3.15 range, AND has the DNS forwarder feature enabled.

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

Apply the relevant Cisco security update or upgrade to a patched IOS/IOS XE version. If patching is delayed, restrict DNS forwarding to trusted internal networks or disable the feature if unnecessary.

Fix this in iOS Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing3.0 h
  • Review / QA1.0 h
10.0 hours of engineering $1,750
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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-2016-6380 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