Cisco Security Advisory
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A vulnerability in the Cisco AnyConnect VPN server of Cisco Meraki MX and Cisco Meraki Z Series Teleworker Gateway devices could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition in the Cisco AnyConnect service on an affected device.
This vulnerability is due to variable initialization errors when an SSL VPN session is established. An attacker could exploit this vulnerability by sending a sequence of crafted HTTPS requests to an affected device. A successful exploit could allow the attacker to cause the Cisco AnyConnect VPN server to restart, resulting in the failure of all established SSL VPN sessions 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, effectively making the Cisco AnyConnect VPN service unavailable for all legitimate users.
Cisco 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-sM5GCfm7
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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 with client certificate authentication enabled:
- MX64
- MX64W
- MX65
- MX65W
- MX67
- MX67C
- MX67W
- MX68
- MX68CW
- MX68W
- MX75
- MX84
- MX85
- MX95
- MX100
- MX105
- MX250
- MX400
- MX450
- MX600
- vMX
- Z3
- Z3C
- Z4
- Z4C
Note: Cisco AnyConnect VPN is supported on Cisco Meraki MX and Cisco Meraki Z Series 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
To determine whether Cisco AnyConnect VPN with client certificate authentication is enabled on a Cisco Meraki MX or Cisco Meraki Z Series device, complete the following steps:
- Log in to the Dashboard.
- The second step differs slightly between platforms and license levels.
- For Cisco Meraki MX devices, choose Security & SD-WAN > Configure > Client VPN in the combined view.
- For Cisco Meraki Z Series devices, 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 and the device is potentially affected by the vulnerability that is described in this advisory. Continue to Step 4.
- If the Cisco AnyConnect Settings tab is not displayed, or if the Disabled radio button is selected, the device is not impacted by this vulnerability.
- Scroll down to the Authentication & policy section.
- If Certificate authentication is set to Enabled, client certificate authentication is enabled and the device is affected by this vulnerability.
- If it is set to Disabled, the device is not impacted by this vulnerability.
Additional Information
Cisco Meraki MX and Cisco Meraki Z Series 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 TLS and Datagram TLS (DTLS) protocols and is commonly referred to as SSL VPN
On both Cisco Meraki MX and Cisco Meraki Z Series devices, Client VPN (L2TP/IPsec) and Cisco AnyConnect VPN (SSL) services can be enabled simultaneously.
Note: This vulnerability resides in the establishment of SSL VPN sessions, 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.
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:
- Adaptive Security Appliance (ASA) Software
- Firepower Threat Defense (FTD) Software
- IOS Software
- IOS XE Software
- Meraki Z1
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There are no workarounds that address this vulnerability.
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Cisco Meraki has released free software updates that address the vulnerability that is described in this advisory. Cisco Meraki recommends that customers upgrade to a fixed release.
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.
In the following table, the left column lists Cisco Meraki firmware releases. The right column indicates whether a release is affected by the vulnerability that is described in this advisory and the first release that includes the fix for this vulnerability. Customers are advised to upgrade to an appropriate fixed software release as indicated in this section.
Cisco Meraki MX Firmware Release First Fixed Release Earlier than 16.2 Not affected. 16.2 Migrate to a fixed release. 17 Migrate to a fixed release. 18.1xx 18.107.13 18.2xx 18.211.6 19.1 19.1.8 Notes:
- Cisco Meraki MX64 and MX65 are affected only when they are running Cisco Meraki MX firmware releases 17.6 and later.
- Cisco Meraki MX400 and MX600 support only firmware releases 16.16.9 and earlier. These models have entered the end-of-life process and will not receive a fix for this vulnerability.
The Cisco Product Security Incident Response Team (PSIRT) validates only the affected and fixed release information that is documented in this advisory.
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The Cisco PSIRT is not aware of any public announcements or 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 1.0 Initial public release. — Final 2025-JUN-18
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