dbcve.org
iOSOperating system · Cisco

CVE-2016-6381

HIGH · 7.5 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 →
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 IOS 12.4 and 15.0 through 15.6 and IOS XE 3.1 through 3.18 and 16.1 allow remote attackers to cause a denial of service (memory consumption or device reload) via fragmented IKEv1 packets, aka Bug ID CSCuy47382.

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 IOS 12.4, 15.0-15.6 and IOS XE 3.1-3.18/16.1 contain a vulnerability in the IKEv1 implementation where specially crafted fragmented packets can cause memory exhaustion or forced device reload, resulting in denial of service.

MitigationApply the relevant Cisco IOS/IOS XE patches from the CSCuy47382 bug report, or implement perimeter filtering to block malformed IKEv1 packet fragments until patching 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
iOSOperating system
Affected:= 12.4\(15\)t7= 12.4\(15\)t8= 12.4\(15\)t9= 12.4\(15\)t10= 12.4\(15\)t11= 12.4\(15\)t12= 12.4\(15\)t13= 12.4\(15\)t14= 12.4\(15\)t15= 12.4\(15\)t16= 12.4\(15\)t17= 12.4\(15\)xl4
Ios XeOperating system
Affected:= 3.1.0s= 3.1.1s= 3.1.2s= 3.1.3as= 3.1.4as= 3.1.4s= 3.2.1s= 3.2.2s= 3.3.0s= 3.3.1s= 3.3.2s= 3.4.0as
Ios Xe 16.1Operating system
Affected:= 16.1.2
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
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
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. Identify the Cisco IOS or IOS XE version
    Run 'show version' on the device console or via SNMP. Look for the version string (e.g., 15.1(4)M, 3.1.0S, etc.)
    Affected if The version matches one of the affected versions listed in the CVE: iOS 12.4(15)T versions t7-t17 or xl4, IOS XE 3.1.xS/3.2.xS/3.3.xS/3.4.xS versions, or IOS XE 16.1.2
  2. Confirm IKEv1 is enabled on the device
    Run 'show running-config | include crypto isakmp' to check for IKEv1 policy configuration, or 'show crypto isakmp sa' to see active IKEv1 Security Associations
    Affected if IKEv1 policies are configured under 'crypto isakmp policy' or active IKEv1 SAs exist in the output
  3. Check if the device processes IPSec VPN traffic
    Run 'show crypto ipsec sa' to inspect IPSec security associations, and review interface configurations for crypto maps applied with 'show crypto map'
    Affected if Crypto maps are applied to interfaces and IPSec SAs are active, indicating the device terminates IKEv1 VPN tunnels
  4. Verify IKEv1 fragmentation handling is occurring
    Monitor with 'show crypto isakmp stats' or check logging/debugging for IKEv1 packet fragments being processed
    Affected if The device is receiving or processing fragmented IKEv1 packets, which triggers the vulnerable code path

The device is affected if it runs an affected Cisco IOS or IOS XE version AND has IKEv1 enabled with active VPN tunnels or IKEv1 traffic being processed.

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 IOS/IOS XE patches from the CSCuy47382 bug report, or implement perimeter filtering to block malformed IKEv1 packet fragments until patching can be completed.

Fix this in iOS Scoped from the published advisory
  • Consultation3.0 h
  • Implementation6.0 h
  • Testing3.0 h
  • Review / QA2.0 h
14.0 hours of engineering $2,490
Get help mitigating

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $3,984.

Scan for this in your stack

Free · runs locally
dbcve dependency scanner

Check whether your project pulls in CVE-2016-6381 — 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-2016-6381 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