VMware Horizon 7.13 Connection Server Security Technical Implementation Guide

The Horizon Connection Server has the ability to limit the number of simultaneous client connections. This capability is helpful in limiting resource exhaustion risks related to denial of service attacks. By default, in code, the Connection Server allows up to 2000 client connections at one time, over all protocol types. For larger deployments, this limit can be increased to a tested and supported maximum of 4000 by making modifications to the "locked.properties" file. Ensure any changes to the number of allowed simultaneous connections is supported by VMware for the choice of protocols and that this value is documented as part of the SSP. Satisfies: SRG-APP-000001-AS-000001, SRG-APP-000435-AS-000163

To ensure that all security-relevant information and events are logged, the Horizon Connection Server must be configured with the "debug" logging level. This is the default value but since it could be changed to "info", this configuration must be verified and maintained.

Role based access and least privilege are two fundamental security concepts that must be properly implemented in Horizon View to ensure the right user and groups have the right permissions on the right objects. Horizon View allows for assigning of roles (pre-defined sets of permissions) to specific users and groups and on a specific Access Group (set of objects). Administrators must ensure that minimal permissions are assigned to the right entities, in the right scope, and stay so over time. Satisfies: SRG-APP-000033-AS-000024, SRG-APP-000118-AS-000078, SRG-APP-000121-AS-000081, SRG-APP-000122-AS-000082, SRG-APP-000123-AS-000083, SRG-APP-000290-AS-000174, SRG-APP-000315-AS-000094, SRG-APP-000340-AS-000185, SRG-APP-000343-AS-000030

The Horizon Connection Server stores application level events and actions in a dedicated database versus log files. This makes day-to-day administration easier while offloading these events to a separate system for resiliency. An events database is configured after Connection Server deployment. It need only be done once, in the case of multiple grouped Connection Servers, as the configuration will be applied to the other servers automatically. Satisfies: SRG-APP-000089-AS-000050, SRG-APP-000091-AS-000052, SRG-APP-000095-AS-000056, SRG-APP-000096-AS-000059, SRG-APP-000097-AS-000060, SRG-APP-000098-AS-000061, SRG-APP-000099-AS-000062, SRG-APP-000100-AS-000063, SRG-APP-000101-AS-000072, SRG-APP-000266-AS-000168, SRG-APP-000380-AS-000088, SRG-APP-000495-AS-000220, SRG-APP-000499-AS-000224, SRG-APP-000503-AS-000228, SRG-APP-000504-AS-000229, SRG-APP-000505-AS-000230, SRG-APP-000509-AS-000234

The Horizon Connection Server comes with pre-defined privileges that can be combined in any combination into a role. That role is then assigned to a user or group. Any role that has the "Manage Global Configuration and Policies" has the ability to change the configuration of the Connection Server, including the events database. This privilege must be restricted and monitored over time.

The Horizon Connection Server performs certificate revocation checking on its own certificate and on those of the security servers paired to it. Each instance also checks the certificates of vCenter and View Composer servers whenever it establishes a connection to them. If a SAML 2.0 authenticator is configured for use by a Connection Server instance, the Connection Server also performs certificate revocation checking on the SAML 2.0 server certificate. By default, all certificates in the chain are checked except the root certificate. This must be changed so that the full path, including the root, is validated.

The Horizon Connection Server can be configured to check the revocation status of PKI certificates over both OCSP and CRL. This capability is disabled by default and must be enabled post-deployment. There are a number of other configurations that are supported, including OCSP and CRL location override but those will be site and architecture specific. The suggested configuration is OCSP with failover to CRL and override the AIA locations via a local OCSP responder, if present. See below: enableRevocationChecking=true ocspCRLFailover=true ocspSendNonce=true enableOCSP=true allowCertCRLs=false crlLocation=http:// ocspURL=http://

If communications sessions remain open for extended periods of time even when unused, there is the potential for an adversary to hijack the session and use it to gain access to the system. Horizon 7 Console sessions can and must be limited in the amount of idle time that will be allowed before automatic logoff. By default, 30 minutes of idle time is allowed but this must be changed to 15 minutes or less for DoD systems. This configuration must be verified and maintained over time. Satisfies: SRG-APP-000220-AS-000148, SRG-APP-000295-AS-000263, SRG-APP-000389-AS-000253

Error logs can contain sensitive information about system errors and system architecture that need to be protected from unauthorized access and modification. By default, Horizon Connection Server logs are only accessible by local windows Administrators. This configuration must be verified and maintained.

Information system logging capability is critical for accurate forensic analysis. Centralized management of log records provides for efficiency in maintenance and management of records, as well as the backup and archiving of those records. The Horizon Connection Server can be configured to send all events to a syslog receiver. Multiple servers can be configured but only the UDP protocol is supported at this time. Satisfies: SRG-APP-000358-AS-000064, SRG-APP-000515-AS-000203

The DoD will only accept PKI certificates obtained from a DoD-approved internal or external certificate authority (CA). If the CA used for verifying the certificate is not DoD-approved, trust of this CA has not been established. The Horizon Connection Server supports the replacement of the default, self-signed certificate with one issued by the DoD. This is accomplished through the normal Windows Server certificate management tools, focusing on the certificate with the "vdm"-friendly name. Satisfies: SRG-APP-000427-AS-000264, SRG-APP-000514-AS-000137

Given the remote access nature of Horizon Connection Server, the client must be ensured to be under positive control as much as is possible from the server side. As such, whenever a network interruption causes a client disconnect, that session must be reauthenticated upon reconnection. To allow a session resumption would be convenient but would allow for the possibility of the endpoint being taken out of the control of the intended user and reconnected to a different network, in control of a bad actor who could then resume the disconnected session.

Horizon Connection Server is intended to provide remote desktops and applications, generally during working hours and for no more than an extended workday. Leaving sessions active for more than what is reasonable for a work day leaves open the possibility of a session becoming unoccupied and insecure on the client side. For example, if a client connection is opened at 0900, there are few day-to-day reasons that the connection should still be open after 1900, therefore the connection must be terminated. If the user is still active, they can reauthenticate immediately and get back on for another ten hours.

Horizon View is intended to provide remote desktops and applications during for more or less continuous use. If an application is open and goes used for more than two hours, that application must be closed to eliminate the risk of that idle application being usurped. For desktops, sessions will not be disconnected after two hours but the credentials stored with Horizon will be invalidated. Subsequent desktop connection attempts will require reauthentication.

Horizon Connection Server caches user credentials temporarily to ensure that the user can connect to their desktop pools without reauthenticating, right after logging in to the broker. However, this grace period must be restricted so that SSO credentials are only retained for 15 minutes before being discarded. Subsequent desktop connection attempts will require reauthentication, even if the user is still connected to the broker.

Horizon Connection Server has the ability to allow clients to authenticate using the local session credentials of their local endpoint. While convenient, this must be disabled for DoD deployments as the server cannot ascertain the method of endpoint login, whether that user's client certificate has since been revoked, etc.

Before clients can pick a desktop or app to access, they must first authenticate to the broker, the Connection Server itself. If the client is accessing the broker directly, then the allowed authentication methods must be specified. These include RADIUS, SecurID, user/pass and smart card. In the DoD, CAC login must be enforced at all times, for all client connections. If the client is connecting through a Security Server or the UAG appliance, this requirement does not apply.

Configuring the application to implement organization-wide security implementation guides and security checklists ensures compliance with federal standards and establishes a common security baseline across DoD that reflects the most restrictive security posture consistent with operational requirements. Configuration settings are the set of parameters that can be changed that affect the security posture and/or functionality of the system. Security-related parameters are those parameters impacting the security state of the application, including the parameters required to satisfy other security control requirements.

Configuring the application to implement organization-wide security implementation guides and security checklists ensures compliance with federal standards and establishes a common security baseline across DoD that reflects the most restrictive security posture consistent with operational requirements. Configuration settings are the set of parameters that can be changed that affect the security posture and/or functionality of the system. Security-related parameters are those parameters impacting the security state of the application, including the parameters required to satisfy other security control requirements.

Configuring the application to implement organization-wide security implementation guides and security checklists ensures compliance with federal standards and establishes a common security baseline across DoD that reflects the most restrictive security posture consistent with operational requirements. Configuration settings are the set of parameters that can be changed that affect the security posture and/or functionality of the system. Security-related parameters are those parameters impacting the security state of the application, including the parameters required to satisfy other security control requirements.

RFC 7034 HTTP Header Field X-Frame-Options, also known as counter clickjacking, is enabled by default on the Horizon Connection Server. It can be disabled by adding the entry "x-frame-options=OFF" to the locked.properties file, usually for troubleshooting purposes. The default configuration must be verified and maintained.

RFC 6454 Origin Checking, which protects against cross-site request forging, is enabled by default on the Horizon Connection Server. When an administrator opens the Horizon 7 Console or a user connects to Blast HTML Access, the server checks that the origin URL for the web request matches the configured secure tunnel URL or "localhost". When the Connection Server is load balanced or front-ended by a Unified Access Gateway (UAG) appliance, origin checking will fail. This is commonly resolved by disabling origin checking entirely by specifying "checkOrigin=false" in the "locked.properties" file. This is not the proper solution. Instead, origin checking must be enabled and the load balancer and UAG appliances must be allowlisted via the "balancedHost" and "portalHost.X" settings in "locked.properties", respectively. Origin checking can be disabled by adding the entry "checkOrigin=false" to locked.properties, usually for troubleshooting purposes. The default, "checkOrigin=true" or unspecified configuration must be verified and maintained.

The Horizon Connection Server Content Security Policy (CSP) feature mitigates a broad class of content injection vulnerabilities, such as cross-site scripting (XSS), clickjacking and other code injection attacks resulting from execution of malicious content in the trusted web page context. The Connection Server defines the policy and the client browser enforces the policy. This feature is enabled by default but must be validated and maintained over time.

The Horizon Connection Server Content Security Policy (CSP) feature mitigates a broad class of content injection vulnerabilities such as cross-site scripting (XSS), clickjacking and other code injection attacks resulting from execution of malicious content in the trusted web page context. The Connection Server has default CSP directives that block XSS attacks, enable x-frame restrictions and more. If the default configurations are overridden, the protections may be disabled even though the CSP itself is still enabled. This default policy must be validated and maintained over time.

The DoD will only accept PKI certificates obtained from a DoD-approved internal or external certificate authority (CA). If the CA used for verifying the certificate is not a DoD-approved CA, trust of this CA has not been established. The Blast Secure Gateway supports the replacement of the default, self-signed certificate with one issued by the DoD. This is accomplished through the normal Windows Server certificate management tools. For simplicity, it is recommended to use the same certificate as previously configured for Connection Server itself via the "vdm" common name.

When the Horizon native smart card capability is not set to "Required", the option for "Unauthenticated Access" is enabled. This would be true in the case of an external IdP providing authentication via SAML. The "Unauthenticated Access" option allows users to access published applications from a Horizon Client without requiring AD credentials. This is typically implemented as a convenience when serving up an application that has its own security and user management. This configuration is not acceptable in the DoD and must be disabled.

If a user VDI session times out due to activity, the user must be assumed to not be active and have their resource locked. These resources should only be made available again upon the user reauthenticating versus reusing the initial connection. This ensures that the connection has not been hijacked and re-stablishes nonrepudiation.

One of the many benefits of VDI is the separation of the end user from the "desktop" they are accessing. This helps mitigate the risks imposed by physical access. In a traditional desktop scenario, and from a security perspective, physical access is equivalent to ownership. USB devices are physical devices that interact at the driver layer with the guest operating system and are inherently problematic. There are numerous risks posed by USB including the driver stack, data loss prevention, malicious devices, etc. Client USB devices are not necessary for general purpose VDI desktops and must be disabled broadly and enabled selectively. Note: USB mouse, keyboard and smart card devices are abstracted by Horizon and are not affected by any of these Horizon configurations.

MIME types define how a given type of file is intended to be processed by the browser. Modern browsers are capable of determining the content type of a file by byte headers and content inspection and can then override the type dictated by the server. An example would be a ".js" that was sent as the "jpg" mime type vs the JavaScript mime type. The browser would "correct" this and process the file as JavaScript. The danger is that a given file could be disguised as something else on the server, like JavaScript, opening up the door to cross-site scripting. To disable browser "sniffing" of content type, the Connection Server sends the "x-content-type-options: nosniff" header by default. This configuration must be validated and maintained over time.