All posts tagged remote code execution

Always On VPN IKEv2 Security Vulnerability April 2026

Microsoft published its Security Updates for April 2026 today, and the good news is that there are no Windows Server Routing and Remote Access (RRAS) vulnerabilities this month. However, they disclosed a critical remote code execution (RCE) vulnerability that impacts deployments using Internet Key Exchange version 2 (IKEv2).

IKE Service Extensions RCE

CVE-2026-33824 addresses a security vulnerability in the Windows Internet Key Exchange (IKE) Service Extensions. This vulnerability is a Remote Code Execution (RCE) vulnerability, with a CVSS 3.1 base score of 9.8 (Critical). Always On VPN implementations that use the device tunnel or IKEv2 for the user tunnel are affected.

Impact

This vulnerability presents a unique challenge to Always On VPN administrators as IKEv2 is required to support device tunnel connections. Some implementations also use IKEv2 for the user tunnel. In either case, the vulnerable VPN server, often domain-joined, is reachable from the Internet, greatly increasing the attack surface and exposure to this vulnerability.

Recommendations

For deployments that use IKEv2 (device or user tunnel), administrators should update their RRAS server as soon as possible to protect against potential attacks on this service.

Not Using IKEv2?

If you are not using the device tunnel or IKEv2 for the user tunnel, ensure the following IKEv2 ports are blocked at the edge firewall.

  • Inbound UDP port 500 (IKE)
  • Inbound UDP port 4500 (IKE NAT-T)

In addition, consider disabling IKEv2 on the RRAS server by opening an elevated command window and running the following command.

netsh.exe ras set wanports device = "WAN Miniport (IKEv2)" rasinonly = disabled ddinout = disabled ddoutonly = disabled maxports = 0

Optionally, you can use the Routing and Remote Access management console (rrasmgnt.msc) to perform this task.

  1. Right-click on Ports and choose Properties.
  2. Select WAN Miniport (IKEv2).
  3. Click Configure.
  4. Uncheck Remote access connections (inbound only).
  5. Uncheck Demand-dial routing connection (inbound and outbound).
  6. Enter 0 in the Maximum ports field.
  7. Click Ok.

Additional Information

Microsoft Security Updates for April 2026

CVE-2026-33824 – Windows Internet Key Exchange (IKE) Service Extension RCE

1 Comment
by Richard M. Hicks on April 14, 2026  •  Permalink
Posted in Always On VPN, AOVPN, CVE, device tunnel, Enterprise, enterprise mobility, IKEv2, Infrastructure, Microsoft, Patch Tuesday, RCE, Remote Access, routing and remote access service, RRAS, Security, Security Update, Update, user tunnel, VPN, Vulnerability, Windows 10, Windows 11, Windows Server 2016, Windows Server 2019, Windows Server 2022, Windows Server 2025
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Posted by Richard M. Hicks on April 14, 2026

https://directaccess.richardhicks.com/2026/04/14/always-on-vpn-ikev2-security-vulnerability-april-2026/

DirectAccess and CVE-2024-38063

With the August 2024 Windows security updates, Microsoft released a fix to address a Remote Code Execution vulnerability in the Windows TCP/IP stack (CVE-2024-38063). Critically, this vulnerability affects IPv6 only and does not require authentication or user interaction to exploit. An attacker would only need to send specially crafted IPv6 packets to a Windows host, which could allow them to run arbitrary code on the server. This vulnerability presents some unique challenges for organizations that have deployed DirectAccess.

Exposure

DirectAccess servers are deployed to provide secure remote access and are, necessarily, exposed to the public Internet. Sometimes, this is a direct connection (not recommended) or behind an edge firewall or load balancer. In either case, anyone can establish a TCP connection from the Internet to the DirectAccess server by default. If the DirectAccess server has a global unicast IPv6 address assigned to its external interface, that presents a worst-case scenario for exposure. Administrators should update their DirectAccess servers immediately. There are some other mitigation options, though. See below for more details.

IPv6 Transition

DirectAccess servers are usually reachable on the public Internet via IPv4 only. The lack of direct IPv6 connectivity significantly reduces the attack vector for this vulnerability. However, DirectAccess servers use various IPv6 transition technologies that could present additional risks.

Tunnel Establishment

Clients on the Internet can establish an IPv6 transition tunnel to the DirectAccess server without authentication. Once the tunnel is established, the client will receive a router advertisement (RA) and establish an IPv6 address on link. However, communication over the link requires IPsec. Although an attacker can obtain an IPv6 address, they require authentication to send TCP and UDP traffic inside the tunnel.

ICMP

It’s important to know that ICMP traffic inside the DirectAccess IPv6 transition tunnel is exempt from IPsec policy processing, by default. It is unclear whether the “specially crafted packets” an attacker must send to exploit this vulnerability can be ICMP packets. If that’s the case, this introduces significant risks and increases exposure exponentially. I will update this post if I learn anything more about this specifically.

Mitigation

The best and most obvious way to mitigate this attack is to immediately apply the Microsoft security updates. However, some additional controls can be effective in mitigating this risk.

Authentication

As mentioned, DirectAccess allows IPv6 transition tunnels to be established by default without authentication. However, it is possible to update the DirectAccess configuration to support authentication, as described here.

https://directaccess.richardhicks.com/2016/06/13/directaccess-ip-https-preauthentication/

Note: Updating the DirectAccess configuration can be impactful for remote users. Be sure to test this change in a lab environment before implementing in production.

Load Balancers

If the DirectAccess server is behind a load balancer, it can be configured to require authentication for DirectAccess IPv6 transition tunnels. Below is published guidance for configuring popular load balancers to support this.

F5 BIG-IP

Citrix ADC (formerly NetScaler)

Additional Information

Microsoft Windows TCP/IP Remote Code Execution Vulnerability

DirectAccess IP-HTTPS Preauthentication

DirectAccess IP-HTTPS Preauthentication using F5 BIG-IP

DirectAccess IP-HTTPS Preauthentication using Citrix ADC (formerly NetScaler)

3 Comments
by Richard M. Hicks on August 15, 2024  •  Permalink
Posted in BIG-IP, CVE, DirectAccess, encapsulation, Enterprise, enterprise mobility, Hotfix, IP-HTTPS, IPv6, Load Balancing, local traffic manager, LTM, Microsoft, Mobility, Operational Support, Remote Access, Security, Security Update, SSL, SSL and TLS, TLS, transition technology, Update, Windows 10, Windows 11, Windows Server 2012 R2, Windows Server 2016, Windows Server 2019, Windows Server 2022, Windows Server 2025
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Posted by Richard M. Hicks on August 15, 2024

https://directaccess.richardhicks.com/2024/08/15/directaccess-and-cve-2024-38063/

Always On VPN Security Updates August 2024

Today is the second Tuesday of the month, so Windows Server administrators everywhere know what that means – it’s Update Tuesday! For Always On VPN administrators in particular there are a few security updates that affect Windows Server Routing and Remote Access (RRAS), which is a popular VPN server used to support Always On VPN implementations. While many of these updates address Remote Code Execution vulnerabilities, non are considered critical.

RRAS Updates

This month there are six vulnerabilities disclosed affecting Windows Server RRAS.

CVE-2024-38120 – Windows RRAS Remote Code Execution Vulnerability (Important)

CVE-2024-38121 – Windows RRAS Remote Code Execution Vulnerability (Important)

CVE-2024-38128 – Windows RRAS Remote Code Execution Vulnerability (Important)

CVE-2024-38130 – Windows RRAS Remote Code Execution Vulnerability (Important)

CVE-2024-38154 – Windows RRAS Remote Code Execution Vulnerability (Important)

CVE-2024-38214 – Windows RRAS Remote Code Execution Vulnerability (Important)

Additional Updates

In addition to the updates addressing vulnerabilities in Windows Server RRAS, there are also updates available for the Windows Network Address Translation (NAT), Windows Transport Layer Security (TLS), and Windows IP Routing Management snapin that could potentially impact Always On VPN deployments.

Recommendations

None of the security vulnerabilities disclosed this month are critical. Although the RRAS vulnerabilities are remote code execution, exploitation is unlikely. However, administrators are encouraged to update their systems as soon as possible.

Additional Information

Microsoft August 2024 Security Updates

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by Richard M. Hicks on August 13, 2024  •  Permalink
Posted in administration, Always On VPN, AOVPN, CVE, Enterprise, Hotfix, Microsoft, Mobility, Operational Support, Remote Access, routing, routing and remote access service, RRAS, Security, Security Update, SSL, SSL and TLS, TLS, Update, VPN, Windows 10, Windows 11, Windows Server 2016, Windows Server 2019, Windows Server 2022
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Posted by Richard M. Hicks on August 13, 2024

https://directaccess.richardhicks.com/2024/08/13/always-on-vpn-security-updates-august-2024/

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