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iOSOperating system · Cisco

CVE-2006-3906

MEDIUM · 5.0 CVSS v2.0 Published 2006-07-27
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
Internet Key Exchange (IKE) version 1 protocol, as implemented on Cisco IOS, VPN 3000 Concentrators, and PIX firewalls, allows remote attackers to cause a denial of service (resource exhaustion) via a flood of IKE Phase-1 packets that exceed the session expiration rate. NOTE: it has been argued that this is due to a design weakness of the IKE version 1 protocol, in which case other vendors and implementations would also be affected.

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

Internet Key Exchange (IKE) version 1 implementation on Cisco IOS, VPN 3000 Concentrators, and PIX firewalls contains a denial of service vulnerability where remote attackers can flood IKE Phase-1 packets exceeding the session expiration rate, causing resource exhaustion.

MitigationImplement rate-limiting on IKE Phase-1 packets at network perimeter devices, and consider migrating to IKEv2 which has improved DoS protection mechanisms.

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:all versions
Vpn 3001 ConcentratorHardware / appliance
Affected:all versions
Vpn 3015 ConcentratorHardware / appliance
Affected:all versions
Vpn 3020 ConcentratorHardware / appliance
Affected:all versions
Vpn 3030 ConcentatorHardware / appliance
Affected:all versions= 4.7\(rel\)= 4.7.1= 4.7.1.f= 4.7.2= 4.7.2.a= 4.7.2.f
Vpn 3060 ConcentratorHardware / appliance
Affected:all versions
Vpn 3080 ConcentratorHardware / appliance
Affected:all versions
Adaptive Security Appliance SoftwareOperating system
Affected:= 7.0= 7.0\(4\)= 7.0\(5\)= 7.0.1.4= 7.0.4.3= 7.1\(2\)

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 the device software version
    Execute 'show version' on the Cisco device CLI to obtain the installed IOS, ASA, or VPN Concentrator software version
    Affected if The version matches any of the affected versions listed (all versions for IOS/3000 concentrators; specific 7.x versions for ASA)
  2. Verify IKEv1 is enabled
    Run 'show running-config | include isakmp' or 'show crypto isakmp sa' to check if IKE/ISAKMP is configured and active
    Affected if IKEv1 (ISAKMP) is enabled and listening on any interface
  3. Confirm IKE is exposed to untrusted networks
    Review interface configurations with 'show ip interface' and check for IKE services bound to external-facing interfaces; examine access-lists for permit rules on UDP port 500 (IKE)
    Affected if IKE is reachable from untrusted or internet-facing networks without adequate rate-limiting controls

The environment is affected if the device runs any affected Cisco software version with IKEv1 enabled and accessible from external networks, making it susceptible to IKE Phase-1 packet flooding DoS attacks.

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

Implement rate-limiting on IKE Phase-1 packets at network perimeter devices, and consider migrating to IKEv2 which has improved DoS protection mechanisms.

Fix this in iOS Scoped from the published advisory
  • Consultation8.0 h
  • Implementation16.0 h
  • Testing8.0 h
  • Review / QA4.0 h
36.0 hours of engineering $6,400
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Scan for this in your stack

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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-2006-3906 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