Cisco Security Advisory
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CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H/E:X/RL:X/RC:X
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A vulnerability in the Cisco AnyConnect VPN server of Cisco Meraki MX and Cisco Meraki Z3 Teleworker Gateway devices could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device.
This vulnerability is due to insufficient validation of client-supplied parameters while establishing an SSL VPN session. An attacker could exploit this vulnerability by crafting a malicious request and sending it to the affected device. A successful exploit could allow the attacker to cause the Cisco AnyConnect VPN server to crash and restart, resulting in the failure of the established SSL VPN connections and forcing remote users to initiate a new VPN connection and re-authenticate. A sustained attack could prevent new SSL VPN connections from being established.
Note: When the attack traffic stops, the Cisco AnyConnect VPN server recovers gracefully without requiring manual intervention.
Cisco Meraki has released software updates that address this vulnerability. There are no workarounds that address this vulnerability.
This advisory is available at the following link: https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-meraki-mx-vpn-dos-vnESbgBf
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Vulnerable Products
This vulnerability affects the following Cisco Meraki products if they are running a vulnerable release of Cisco Meraki MX firmware and have Cisco AnyConnect VPN enabled:
- MX64
- MX64W
- MX65
- MX65W
- MX67
- MX67CW
- MX67W
- MX68
- MX68CW
- MX68W
- MX75
- MX84
- MX85
- MX95
- MX100
- MX105
- MX250
- MX400
- MX450
- MX600
- vMX
- Z3C
- Z3
Note: Cisco AnyConnect VPN is supported on Cisco Meraki MX Series and Cisco Meraki Z3 Teleworker Gateway devices that run Cisco Meraki MX firmware releases 16.2 and later, except for Cisco Meraki MX64 and MX65, which support Cisco AnyConnect VPN only if they are running Cisco Meraki MX firmware releases 17.6 and later.
For information about which Cisco software releases are vulnerable, see the Fixed Software section of this advisory.
Determine the Device Configuration
Determine Whether Cisco AnyConnect VPN Is Enabled on Cisco Meraki MX Devices
To determine whether Cisco AnyConnect VPN is enabled on a Cisco Meraki MX device, complete the following steps:
- Log in to the Dashboard.
- Choose Security Appliance > Configure > Client VPN in the combined view.
- Choose the AnyConnect Settings tab.
If the Enabled radio button is selected, the device is configured to support Cisco AnyConnect VPN.
If the Cisco AnyConnect Settings tab is not displayed, or if the Disabled radio button is selected, the device is not impacted by the vulnerability described in this advisory.
Determine Whether Cisco AnyConnect VPN Is Enabled on Cisco Meraki Z3 Teleworker Gateway Devices
To determine whether Cisco AnyConnect VPN is enabled on Cisco Meraki Z3 Teleworker Gateway devices, complete the following steps:
- Log in to the Dashboard.
- Choose Teleworker gateway > Configure > Client VPN in the combined view.
- Choose the AnyConnect Settings tab.
If the Enabled radio button is selected, the device is configured to support Cisco AnyConnect VPN.
If the Cisco AnyConnect Settings tab is not displayed, or if the Disabled radio button is selected, the device is not impacted by the vulnerability described in this advisory.
Products Confirmed Not Vulnerable
Only products listed in the Vulnerable Products section of this advisory are known to be affected by this vulnerability.
Cisco has confirmed that this vulnerability does not affect the following Cisco products:
- Meraki MX 60
- Meraki MX 80
- Meraki MX 90
- Meraki Z1
- Adaptive Security Appliance (ASA) Software
- Firepower Threat Defense (FTD) Software
- IOS Software
- IOS XE Software
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Cisco Meraki MX Series and Cisco Meraki Z3 Teleworker Gateway devices support the following two VPN services for remote network access:
- Client VPN, which uses Layer 2 Tunneling Protocol (L2TP) or IPsec tunneling protocols
- Cisco AnyConnect VPN, which uses Transport Layer Security (TLS) and Datagram TLS (DTLS) protocols and is commonly referred to as SSL VPN
On both Cisco Meraki MX Series and Cisco Meraki Z3 Teleworker Gateway devices, Client VPN (L2TP/IPsec) and Cisco AnyConnect VPN (SSL) services can be enabled simultaneously.
This vulnerability resides in the processing of TLS and DTLS packets, so it affects only devices that are configured with Cisco AnyConnect VPN. Devices that are configured to provide remote network access exclusively through Client VPN (L2TP/IPsec) are not affected by this vulnerability.
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There are no workarounds that address this vulnerability. Cisco Meraki recommends that administrators upgrade devices to a fixed software release. Disabling Cisco AnyConnect VPN will remove the attack vector for the vulnerability that is described in this advisory.
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Cisco Meraki has released free software updates that address the vulnerability that is described in this advisory.
Customers may only install and expect support for software releases and feature sets for which they have purchased a license. By installing, downloading, accessing, or otherwise using such software upgrades, customers agree to follow the terms of the Cisco End User License Agreement and applicable Product Specific Terms:
https://www.cisco.com/c/en/us/products/end-user-license-agreement.htmlAdditionally, customers may only download software for which they have a valid license, procured from Cisco Meraki directly, or through a Cisco Meraki authorized reseller or partner. In most cases, this will be a maintenance upgrade to software that was previously purchased. Free security software updates do not entitle customers to a new software license, additional software feature sets, or major revision upgrades.
Customers are advised to regularly consult the advisories for Cisco Meraki products, which are available from the Cisco Security Advisories page, to determine exposure and a complete upgrade solution.
In all cases, customers should ensure that the devices to be upgraded contain sufficient memory and confirm that current hardware and software configurations will continue to be supported properly by the new release. Cisco Meraki recommends utilizing firmware best practices for firmware updates. If the information is not clear, customers are advised to contact Cisco Meraki Support.
Fixed Releases
At the time of publication, the release information in the following table was accurate. Cisco Meraki will update this advisory as required.
The left column lists Cisco Meraki MX firmware releases, and the right column indicates whether a release was affected by the vulnerability described in this advisory and which release included the fix for this vulnerability. Both Cisco Meraki MX Series and Cisco Meraki Z3 Teleworker Gateway run Cisco Meraki MX firmware. Therefore, information in the following table applies to both platforms.
Cisco Meraki MX Firmware Release Fixed Release for This Vulnerability Earlier than 16.2 Not affected 16.2 and later 16.16.6 17.x 17.10.1
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Neither the Cisco Product Security Incident Response Team (PSIRT) nor the Cisco Meraki Incident Response Team is aware of any malicious use of the vulnerability that is described in this advisory.
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This vulnerability was found during the resolution of a Cisco Meraki support case.
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To learn about Cisco security vulnerability disclosure policies and publications, see the Security Vulnerability Policy. This document also contains instructions for obtaining fixed software and receiving security vulnerability information from Cisco.
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Show LessVersion Description Section Status Date 1.1 Changed advisory status from interim to final. Header Final 2022-OCT-19 1.0 Initial public release. — Interim 2022-OCT-19
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