# What is CVE-2006-3906?

> CVE-2006-3906 is a medium-severity flaw (CVSS 5.0) in IOS from Cisco, published on 27 July 2006. It is not on the list of flaws known to be exploited today. The latest forecast puts its chance of use in the next 30 days at 6.9%. If you run an affected version, plan in the vendor’s fix.

Canonical page: https://www.precursorintelligence.com/what-is/cve-2006-3906

## At a glance

- **Verdict:** Plan it in. No sign of exploitation and a low forecast. Patch it in your normal update cycle.
- **Precursor Intelligence risk score:** 23 out of 100 (Low); action: Monitor. Kept up to date as the evidence changes.
- **Severity:** Medium (CVSS 5.0 out of 10)
- **Known to be exploited:** No, not on the list of flaws known to be exploited today
- **Chance of use in the next 30 days:** 6.9% (latest exploit-likelihood forecast)
- **Published:** 27 July 2006
- **Record last updated:** 16 June 2026
- **Main product:** IOS from Cisco
- **Affected products:** 21

## What is CVE-2006-3906? In plain terms

It can be attacked from anywhere on the internet without logging in. If it works, the attacker can slow it down.

### The official description

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.

### What kind of flaw is it?

- Unknown: Unknown

### How an attack on it works

- Where an attacker can be: Anywhere on the internet
- How hard it is to pull off: Easy: no special conditions
- Login needed first: No login needed
- What an attacker gets: Can slow it down

Severity vector: `AV:N/AC:L/Au:N/C:N/I:N/A:P`

## Is CVE-2006-3906 being exploited? Not that we know of

It is not on the list of flaws known to be exploited today. The latest forecast puts the chance of it being used in the next 30 days at 6.9%. That can change at any time, which is why we keep watching.

Exploit likelihood over the last 7 days: 6.9%, 6.9%, 6.9%, 6.9%, 6.9%, 6.9%, 6.9%.

### Timeline

- 27 July 2006: Published
- 16 June 2026: Record last updated

### How Precursor Intelligence ranks it

CVE-2006-3906 scores **23 out of 100 (Low)**, with the action "Monitor".

Every published flaw gets a risk score from 0 to 100, kept up to date as the evidence changes. Four things go into the score, from the one that counts most to the ones that count less:

- Evidence it is being exploited: biggest factor
- How severe it is: strong factor
- How widely exposed it is: smaller factor
- Threat activity around it: smaller factor

85 and above is Critical. Anything confirmed as exploited is always marked for an emergency patch, whatever its score. When this flaw matches software you track, it lands in your list with its score and the reasons behind it.

## Who is affected by CVE-2006-3906?

The published record lists 21 products.

- [IOS](https://www.precursorintelligence.com/product/cisco/ios) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): all versions
- [Pix Firewall Software](https://www.precursorintelligence.com/product/cisco/pix_firewall_software) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 2.7, 3.0, 3.1, 4.1(6b), 4.1(6), 4.2(1), 4.2(2), 4.2(5), 4.4(4), 4.4(7.202), 4.4(8), 4.0, 4.2, 4.3, 4.4, 5.1(4.206), 5.1(4), 5.2(1), 5.2(2), 5.2(3.210), 5.2(5), 5.2(6), 5.2(7), 5.2(9), 5.3(1.200), 5.3(1), 5.3(2), 5.3(3), 5.0, 5.1, 5.2, 5.3, 6.0(1), 6.0(2), 6.0(3), 6.0(4.101), 6.0(4), 6.1(1), 6.1(2), 6.1(3) and 17 more
- [VPN 3000 Concentrator Series Software](https://www.precursorintelligence.com/product/cisco/vpn_3000_concentrator_series_software) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 2.0, 2.5.2.a, 2.5.2.b, 2.5.2.c, 2.5.2.d, 2.5.2.f, 3.1(rel), 3.5(rel), 3.0, 3.0.3.a, 3.0.3.b, 3.0.4, 3.1, 3.1.1, 3.1.2, 3.1.4, 3.5.1, 3.5.2, 3.5.3, 3.5.4, 3.5.5, 3.6, 3.6.1, 3.6.3, 3.6.5, 3.6.7.a, 3.6.7.b, 3.6.7, 3.6.7.c, 3.6.7.d, 3.6.7d, 3.6.7.f, 4.7(rel), 4.0, 4.0.1, 4.0.2, 4.0.5.b, 4.1, 4.1.5.b, 4.1.7.a and 8 more
- [VPN 3030 Concentator](https://www.precursorintelligence.com/product/cisco/vpn_3030_concentator) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Hardware): all versions, 4.7(rel), 4.7.1, 4.7.1.f, 4.7.2.a, 4.7.2, 4.7.2.f
- [Adaptive Security Appliance Software](https://www.precursorintelligence.com/product/cisco/adaptive_security_appliance_software) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 7.0(4), 7.0(5), 7.1(2), 7.0, 7.0.1.4, 7.0.4.3
- [Pix Firewall](https://www.precursorintelligence.com/product/cisco/pix_firewall) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Application): 6.2.2_.111, 6.2.3_(110), 6.3.3_(133), 6.3.5_(112)
- [Pix ASA IDS](https://www.precursorintelligence.com/product/cisco/pix_asa_ids) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Application): all versions
- [Pix Firewall 501](https://www.precursorintelligence.com/product/cisco/pix_firewall_501) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Hardware): all versions
- [Pix Firewall 506](https://www.precursorintelligence.com/product/cisco/pix_firewall_506) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Hardware): all versions
- [Pix Firewall 515](https://www.precursorintelligence.com/product/cisco/pix_firewall_515) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Hardware): all versions
- [Pix Firewall 515e](https://www.precursorintelligence.com/product/cisco/pix_firewall_515e) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Hardware): all versions
- [Pix Firewall 520](https://www.precursorintelligence.com/product/cisco/pix_firewall_520) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Hardware): all versions
- [Pix Firewall 525](https://www.precursorintelligence.com/product/cisco/pix_firewall_525) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Hardware): all versions
- [Pix Firewall 535](https://www.precursorintelligence.com/product/cisco/pix_firewall_535) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Hardware): all versions
- [Secure Pix Firewall](https://www.precursorintelligence.com/product/cisco/secure_pix_firewall) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Hardware): all versions
- [VPN 3001 Concentrator](https://www.precursorintelligence.com/product/cisco/vpn_3001_concentrator) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Hardware): all versions
- [VPN 3005 Concentrator Software](https://www.precursorintelligence.com/product/cisco/vpn_3005_concentrator_software) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 4.0.1
- [VPN 3015 Concentrator](https://www.precursorintelligence.com/product/cisco/vpn_3015_concentrator) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Hardware): all versions
- [VPN 3020 Concentrator](https://www.precursorintelligence.com/product/cisco/vpn_3020_concentrator) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Hardware): all versions
- [VPN 3060 Concentrator](https://www.precursorintelligence.com/product/cisco/vpn_3060_concentrator) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Hardware): all versions
- [VPN 3080 Concentrator](https://www.precursorintelligence.com/product/cisco/vpn_3080_concentrator) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Hardware): all versions

## How do I fix CVE-2006-3906?

1. **Check whether you run it.** Compare your versions with the affected products above. Not sure what you run? Precursor Intelligence can work it out from your public website, or you can pick it from a list.
2. **Apply the vendor’s fix.** Install the latest update from the vendor. The references list where the vendor has published details.
3. **If you can’t patch today.** Follow any mitigation the vendor publishes, and limit who can reach the affected system from the internet until the update is in.
4. **Keep an eye on it.** Track the product and we tell you as soon as we spot this flaw on the list of exploited flaws, or a jump in its exploit likelihood.

### References

- [archives.neohapsis.com](http://archives.neohapsis.com/archives/bugtraq/2006-07/0531.html)
- [securityreason.com](http://securityreason.com/securityalert/1293)
- [securitytracker.com](http://securitytracker.com/id?1016582)
- [cisco.com](http://www.cisco.com/en/US/tech/tk583/tk372/tsd_technology_security_response09186a00806f33d4.html)
- [nta-monitor.com](http://www.nta-monitor.com/posts/2006/07/cisco-concentrator-dos.html)
- [osvdb.org](http://www.osvdb.org/29068)
- [securityfocus.com](http://www.securityfocus.com/archive/1/441203/100/0/threaded)
- [securityfocus.com](http://www.securityfocus.com/bid/19176)
- [exchange.xforce.ibmcloud.com](https://exchange.xforce.ibmcloud.com/vulnerabilities/27972)
- [oval.cisecurity.org](https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A5299)

## Questions

### What is CVE-2006-3906?

CVE-2006-3906 is a medium-severity flaw in IOS from Cisco, published on 27 July 2006. It can be attacked from anywhere on the internet without logging in. If it works, the attacker can slow it down.

### How serious is CVE-2006-3906?

It scores 5.0 out of 10 on the CVSS severity scale, which is medium. Our risk score for CVE-2006-3906 is 23 out of 100, which is Low. Its action is "Monitor". No sign of exploitation and a low forecast. Patch it in your normal update cycle.

### Is CVE-2006-3906 being exploited?

It is not on the list of flaws known to be exploited today. The latest forecast puts the chance of it being used in the next 30 days at 6.9%. That can change at any time, which is why we keep watching.

### Which versions does CVE-2006-3906 affect?

For IOS from Cisco: all versions. The record lists 21 products in all, each with its versions, under "Who is affected" on this page.

### How do I fix CVE-2006-3906?

Install the update the vendor names in its advisory. If you can't patch today, follow the vendor's mitigation and limit who can reach the affected system from the internet.

## Does CVE-2006-3906 affect you?

Precursor Intelligence keeps checking for you:

- **Tell us what you run.** Pick your software from a list, or let us work it out from your website.
- **We match it to every flaw.** Over 400,000 published flaws, checked against your list.
- **Ranked by real-world risk.** Every flaw gets a 0 to 100 risk score, kept up to date, led by evidence criminals are using it.
- **Told as soon as we know.** An alert by email, in the app or by webhook to your own tools.

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