Some older protocols and ciphers that are no longer considered secure are disabled in VMware Horizon by default. If required, you can enable them manually.

Disabled Protocols and Ciphers

In VMware Horizon, the following protocols and ciphers are disabled by default:

DHE Cipher Suites

Cipher suites that are compatible with DSA certificates use Diffie-Hellman ephemeral keys, and these suites are no longer enabled by default, starting with Horizon 6 version 6.2. For more information, see http://kb.vmware.com/kb/2121183.

For Connection Server instances and VMware Horizon desktops, you can enable these cipher suites by editing the Horizon LDAP database, locked.properties file, or registry, as described in this guide. See Change the Global Acceptance and Proposal Policies, Configure Acceptance Policies on Individual Servers, and Configure Proposal Policies on Remote Desktops. You can define a list of cipher suites that includes one or more of the following suites, in this order:

  • TLS_DHE_DSS_WITH_AES_128_GCM_SHA256 (TLS 1.2 only, not FIPS)
  • TLS_DHE_DSS_WITH_AES_256_GCM_SHA384 (TLS 1.2 only, not FIPS)
  • TLS_DHE_DSS_WITH_AES_128_CBC_SHA256 (TLS 1.2 only)
  • TLS_DHE_DSS_WITH_AES_128_CBC_SHA
  • TLS_DHE_DSS_WITH_AES_256_CBC_SHA256 (TLS 1.2 only)
  • TLS_DHE_DSS_WITH_AES_256_CBC_SHA

For Horizon Agent Direct-Connection Plug-In machines, you can enable DHE cipher suites by adding the following to the list of ciphers when you follow the procedure "Disable Weak Ciphers in SSL/TLS for Horizon Agent Machines" in the Horizon Installation and Upgrade document. 

TLS_DHE_RSA_WITH_AES_256_GCM_SHA384
TLS_DHE_RSA_WITH_AES_128_GCM_SHA256
Note: It is not possible to enable support for ECDSA certificates. These certificates have never been supported.

SHA-1

In FIPS mode, certificate verification will fail with "Certificates do not conform to algorithm constraints" if a certificate is signed using SHA-1. This applies to any certificate in the chain, including the root certificate. For more information about why this signature algorithm is deprecated, see https://cabforum.org/wp-content/uploads/BRv1.2.5.pdf.

Replace failing certificates if possible. If this cannot be done, SHA-1 signatures can be re-enabled by making an LDAP edit. Navigate to CN=Common,OU=Global,OU=Properties,DC=vdi,DC=vmware,DC=int. Modify attribute pae-SSLClientSignatureSchemes by adding rsa_pkcs1_sha1 to the list of comma-separated values. Save the modified attribute and then restart the Connection Server service on each Connection Server in the cluster, one at a time.

No Forward Secrecy (PFS)

For more information, see https://datatracker.ietf.org/doc/html/rfc7525. Cipher suites specifying key exchange algorithms that do not exhibit forward secrecy (PFS) are disabled by default. For instructions on how to enable these cipher suites, see the other sections of this topic.

Re-enabling Protocols

Although the protocols listed above have been deprecated for good reasons, you might have a use case where you need to re-enable one or more of them. If so, you can enable protocols by following the procedure below.

For Connection Server instances and VMware Horizon desktops, you can enable a protocol on a Connection Server or a Horizon Agent machine by editing the configuration file C:\Program Files\VMware\VMware View\Server\jre\conf\security\java.security. At the end of the file is a multi-line entry called jdk.tls.legacyAlgorithms. Remove the protocol and the comma that follows it from this entry and restart the Connection Server or the Horizon Agent machine.

Also see the section "Enable TLSv1 on vCenter Connections from Connection Server" in the Horizon Installation and Upgrade document.

For Horizon Agent Direct-Connection (formerly VADC) machines, you can enable a protocol by adding a line to the list of ciphers when you follow the procedure "Disable Weak Ciphers in SSL/TLS Horizon Agent Machines" in the Horizon Installation and Upgrade document. For example, to enable RC4, you can add the following.

TLS_RSA_WITH_RC4_128_SHA