Applies To:

Show Versions Show Versions

Manual Chapter: Additional SSL Profile Configuration Options
Manual Chapter
Table of Contents   |   << Previous Chapter   |   Next Chapter >>

Additional SSL Profile Configuration Options

Options

OpenSSL supports a set of SSL options and defect workarounds. You can enable these workarounds and options as settings of an individual client-side or server-side SSL profile. The default value for the Options setting is Options List. Retaining the default value enables one option, which is Don’t insert empty fragments. You can then enable other options that appear in the Available Options list.

Important: For security reasons, when you enable the Proxy SSL setting, the BIG-IP® system automatically disables the Don’t insert empty fragments option. Disabling this option when Proxy SSL is enabled guards against a particular type of cryptographic attack.

Note that when configuring protocol versions, you must ensure that the protocol versions configured for the BIG-IP system match those of the system’s peer. That is, protocol versions specified in the client-side SSL profile must match those of the client, and protocol versions specified in the server-side SSL profile must match those of the server. Thus, for both client-side and server-side SSL connections, you can specify the protocol versions that you do not want the BIG-IP system to allow.

Note: F5 Networks recommends that, at a minimum, you specify protocol version SSLv2 as invalid.

Workarounds and other SSL options

This table lists and describes the possible workarounds and options that you can configure for an SSL profile.

SSL Attribute Description
Cipher server preference When the BIG-IP® system chooses a cipher, this option uses the server's preferences instead of the client preferences. When this option is not set, the SSL server always follows the client’s preferences. When this option is set, the SSLv3/TLSv1 server chooses by using its own preferences. Due to the different protocol, for SSLv2 the server sends its list of preferences to the client, and the client always chooses the cipher.
Don’t insert empty fragments This option disables a countermeasure against a SSL 3.0/TLS 1.0 protocol vulnerability affecting CBC ciphers. These ciphers cannot be handled by certain broken SSL implementations. This option has no effect for connections using other ciphers. This is the default value for the Options list.
Note: For security reasons, this option is not available when you enable the Proxy SSL setting.
Ephemeral RSA This option uses ephemeral (temporary) RSA keys when doing RSA operations. According to the specifications, this is only done when an RSA key can only be used for signature operations (namely under export ciphers with restricted RSA key length). By setting this option, Local Traffic Manager™ always uses ephemeral RSA keys. This option breaks compatibility with the SSL/TLS specifications and can lead to interoperability problems with clients, and we therefore do not recommend it. You should use ciphers with EDH (ephemeral Diffie-Hellman) key exchange instead. This option is ignored for server-side SSL.
Microsoft session ID bug This option handles a Microsoft® session ID problem.
Netscape CA DN bug workaround This option handles a defect regarding system instability. If the system accepts a Netscape® browser connection, demands a client cert, has a non-self-signed CA that does not have its CA in Netscape, and the browser has a certificate, then the system crashes or hangs.
Netscape challenge bug This option handles the Netscape challenge problem.
Netscape demo cipher change bug workaround This option deliberately manipulates the SSL server session resumption behavior to mimic that of certain Netscape servers (see the Netscape reuse cipher change bug workaround description). We do not recommend this option for normal use and it is ignored for server-side SSL processing.
Netscape reuse cipher change bug workaround This option handles a defect within Netscape-Enterprise/2.01, only appearing when connecting through SSLv2/v3 then reconnecting through SSLv3. In this case, the cipher list changes. First, a connection is established with the RC4-MD5 cipher list. If it is then resumed, the connection switches to using the DES-CBC3-SHA cipher list. However, according to RFC 2246, (section 7.4.1.3, cipher_suite) the cipher list should remain RC4-MD5. As a workaround, you can attempt to connect with a cipher list of DES-CBC-SHA:RC4-MD5 and so on. For some reason, each new connection uses the RC4-MD5 cipher list, but any re-connect ion attempts to use the DES-CBC-SHA cipher list. Thus Netscape, when reconnecting, always uses the first cipher in the cipher list.
No SSL Do not use the SSL protocol.
No SSLv2 Do not use the SSLv2 protocol.
No SSLv3 Do not use the SSLv3 protocol.
No session resumption on renegotiation When Local Traffic Manager performs renegotiation as an SSL server, this option always starts a new session (that is, session resumption requests are only accepted in the initial handshake). The system ignores this option for server-side SSL processing.
No TLS Do not use the TLS protocol.
No TLSv1 Do not use the TLSv1 protocol.
Microsoft big SSLV3 buffer This option enables a workaround for communicating with older Microsoft® applications that use non-standard SSL record sizes.
Microsoft IE SSLV2 RSA padding This option enables a workaround for communicating with older Microsoft® applications that use non-standard RSA key padding. This option is ignored for server-side SSL.
Passive close Specifies that the SSL filter helps prevent packets from getting into the TCP half-closed state by waiting for a connection shutdown from the server. This is a workaround for HTTP/1.0 and HTTP/0.9 clients that send an HTTP request followed by a FIN, which immediately closes the connection for server-SSL-only proxies. Instead of closing immediately, the proxy waits for the server to close.
PKCS1 check 1 This debugging option deliberately manipulates the PKCS1 padding used by SSL clients in an attempt to detect vulnerability to particular SSL server vulnerabilities. We do not recommend this option for normal use. The system ignores this option for client-side SSL processing.
PKCS1 check 2 This debugging option deliberately manipulates the PKCS1 padding used by SSL clients in an attempt to detect vulnerability to particular SSL server vulnerabilities. We do not recommend this option for normal use. The system ignores this option for client-side SSL processing.
Single DH use This option creates a new key when using temporary/ephemeral DH parameters. You must use this option if you want to prevent small subgroup attacks, when the DH parameters were not generated using strong primes (for example, when using DSA-parameters). If strong primes were used, it is not strictly necessary to generate a new DH key during each handshake, but we do recommend this. You should enable the Single DH use option whenever temporary/ephemeral DH parameters are used.
SSLEAY 080 client DH bug workaround This option enables a workaround for communicating with older SSLeay-based applications that specify an incorrect Diffie-Hellman public value length. This option is ignored for server-side SSL.
SSL Ref2 reuse cert type bug This option handles the SSL re-use certificate type problem.
TLS D5 bug workaround This option is a workaround for communicating with older TLSv1-enabled applications that specify an incorrect encrypted RSA key length. This option is ignored for server-side SSL.
TLS block padding bug workaround This option enables a workaround for communicating with older TLSv1-enabled applications that use incorrect block padding.
TLS rollback bug workaround This option disables version rollback attack detection. During the client key exchange, the client must send the same information about acceptable SSL/TLS protocol levels as it sends during the first hello. Some clients violate this rule by adapting to the server's answer. For example, the client sends an SSLv2 hello and accepts up to SSLv3.1 (TLSv1), but the server only understands up to SSLv3. In this case, the client must still use the same SSLv3.1 (TLSv1) announcement. Some clients step down to SSLv3 with respect to the server's answer and violate the version rollback protection. This option is ignored for server-side SSL.

ModSSL methods

You can enable or disable ModSSL method emulation. You enable ModSSL method emulation when the OpenSSL methods are inadequate. When you enable this setting, you can then write an iRule, using the HTTP::header insert_modssl_fields command, which inserts some of the ModSSL options as headers into HTTP requests.

ModSSL options for use with iRules

This table lists the options that you can insert into an HTTP request.

Header Type Header Name and Format Description
Certificate status SSLClientCertStatus: [status] The status of the client certificate. The value of [status] can be NoClientCert, OK, or Error. If status is NoClientCert, only this header is inserted into the request. If status is Error, the error is followed by a numeric error code.
Certificate version SSLClientCertVersion: [version] The version of the certificate.
Certificate serial number SSLClientCertSerialNumber: [serial] The serial number of the certificate.
Signature algorithm of the certificate SSLClientCertSignatureAlgorithm: [alg] The signature algorithm of the certificate.
Issuer of the certificate SSLClientCertIssuer: [issuer] The issuer of the certificate.
Certificate validity dates SSLClientCertNotValidBefore: [before] SSLClientCertNotValidAfter: [after] The validity dates for the certificate. The certificate is not valid before or after the dates represented by [before] and [after], respectively.
Certificate subject SSLClientCertSubject: [subject] The subject of the certificate.
Public key of the subject SSLClientCertSubjectPublicKey: [key] The type of public key type. The allowed types are RSA ([size] bit), DSA, or Unknown public key.
The certificate itself SSLClientCert: [cert] The actual client certificate.
MD5 hash of the certificate SSLClientCertHash: [hash] The MD5 hash of the client certificate.

SSL session cache size and timeout

You can configure timeout and size values for the SSL session cache. Because each profile maintains a separate SSL session cache, you can configure the values on a per-profile basis.

SSL session cache size

You can specify the maximum size of the SSL session cache. The default value for the size of the SSL session cache is 262144 entries. A value of 0 disallows session caching.

SSL session cache timeout

You can specify the number of usable lifetime seconds of negotiated SSL session IDs. The default timeout value for the SSL session cache is 3600 seconds. If you specify a timeout value, valid values are integers greater than or equal to 1.

Clients attempting to resume an SSL session with an expired session ID are forced to negotiate a new session.

Warning: If the timeout value for the client-side SSL session cache is set to zero, the SSL session IDs negotiated with that profile’s clients remain in the session cache until the cache is filled and the purging of entries begins. Setting a value of zero can introduce a significant security risk if valuable resources are available to a client that is reusing those session IDs. It is therefore common practice to set the SSL session cache timeout to a length of time no greater than 24 hours, and for significantly shorter periods.

Alert timeout

You can specify the duration in seconds that the BIG-IP® system waits while trying to close an SSL connection, before the connection is reset. The default timeout value for this setting is 10 seconds.

Handshake timeout

You can specify the amount of time in seconds that the BIG-IP® system spends attempting to perform an SSL handshake. The default timeout value for this setting is 10 seconds.

Renegotiation of SSL sessions

Long-lived connections are susceptible to man-in-the-middle attacks. To prevent such attacks, you can force the BIG-IP® system to renegotiate SSL sessions, based on either time period or application size. You can also force the BIG-IP system to terminate an SSL session after receiving a specified number of records.

More specifically, you can control, on a per-connection basis, the way that the system responds to mid-stream SSL reconnection requests. When you enable renegotiation, the system processes mid-stream SSL renegotiation requests. When you disable renegogiation, the system either terminates the connection or ignores the request, depending on the system configuration. By default, renegotiation is enabled.

Sessions based on a time period

You can specify the number of seconds from the initial connect time that the system renegotiates an SSL session. The options are a number you specify, indefinite, and default. The default is indefinite, meaning that you do not want the system to renegotiate SSL sessions. Each time the session renegotiation is successful, essentially a new connection is started. Therefore, the system attempts to renegotiate the session again in the specified amount of time following the successful session renegotiation. For example, setting the renegotiate period to 3600 seconds triggers session renegotiation at least once an hour.

Sessions based on application data size

You can force Local Traffic Manager™ to renegotiate an SSL session after the specified number of megabytes of application data have been transmitted over the secure channel. The default value for this setting is Indefinite.

Maximum record delay

You can force Local Traffic Manager™ (LTM®) to terminate an SSL session after receiving the specified maximum number of delayed SSL records. If LTM receives more than the specified number of delayed SSL records, the system closes the connection. The default value for this setting is Indefinite.

Secure renegotiation

The Secure Renegotiation setting specifies the method of secure renegotiation for SSL connections. The default value for the Client SSL profile is Require; the default value for the Server SSL profile is Require Strict. If your configuration does not require secure SSL renegotiation, set this value to Request. The possible values for this setting are:

Request
Specifies that the system requests secure renegotiation of SSL connections.
Require
Specifies that the system requires secure renegotiation of SSL connections. In this mode, the system permits initial SSL handshakes from clients, but terminates renegotiations from unpatched clients.
Require Strict
Specifies that the system requires strict secure renegotiation of SSL connections. In this mode, the system refuses new SSL connections to unsecure servers and terminates existing SSL connections to unsecure servers.

Maximum reneogtiations

You can specify the maximum number of SSL records per minute that the system can receive before renegotiating an SSL session. After receiving this number of SSL records, the system closes the connection. This setting applies to client profiles only. By default, the system receives five records per minute before reneogiating the session.

Maximum aggregate renegotiations

You can specify a maximum number of aggregate SSL renegotiations, to ensure that the configured per-flow maximum renegotiation rate limit is enforced. Specifying a maximum number of aggregate renegotiations prevents the opening of new connections as a way to bypass the per-flow limit. Allowed values are from 0 through 0xFFFFFFFF.

Server name

The Server Name setting in an SSL profile specifies the name of the specific domain from which the client requests a certificate. This setting supports a feature known as TLS Server Name Indication (TLS SNI), used when a single virtual IP server needs to host multiple domains.

For example, suppose that the BIG-IP® system needs to host the two domains domain1.com and domain2.com, on the same HTTP virtual server. Each domain has its own server certificate to use, such as domain1.crt and domain2.crt, and each has different security requirements.

To ensure that the BIG-IP system presents the correct certificate to the browser, you enable SNI, which sends the name of a domain as part of the TLS negotiation. This, in turn, enables the BIG-IP system to select this domain rather than waiting to read the domain name in the request header.

To enable SNI, you configure the Server Name and other TLS-related settings on an SSL profile, and then assign the profile to a virtual server.

Note that the wildcard character (*) is supported within any domain name that you specify.

Default SSL Profile for SNI

When you enable the Default SSL Profile for SNI setting on an SSL profile, you are specifying that this is the default SSL profile to use when the client provides either no Server Name Indication (SNI) extension, or provides a non-matching SNI extension.

When assigning multiple SSL profiles to a single virtual server, you can enable this setting on one Client SSL profile only and one Server SSL profile only.

Require Peer SNI Support

If you enable the Require Peer SNI Support setting on an SSL profile, the domain name of the peer must match the domain name that you specify in the Default SSL Profile for SNI field.

Unclean SSL shutdowns

In an unclean shutdown, underlying TCP connections are closed without exchanging the required SSL shutdown alerts. However, you can disable unclean shutdowns and thus force the SSL profile to perform a clean shutdown of all SSL connections by configuring this setting.

This feature is especially useful with respect to the Internet Explorer browser. Different versions of the browser, and even different builds within the same version of the browser, handle shutdown alerts differently. Some versions or builds require shutdown alerts from the server, while others do not, and the SSL profile cannot always detect this requirement or lack of it. In the case where the browser expects a shutdown alert but the SSL profile has not exchanged one (the default setting), the browser displays an error message.

By default, this setting is enabled, which means that Local Traffic Manager™ performs unclean shutdowns of all SSL connections.

Strict Resume

You can configure Local Traffic Manager™ to discontinue an SSL session after an unclean shutdown. By default, this setting is disabled, which causes Local Traffic Manager (LTM®) to resume SSL sessions after an unclean shutdown. If you enable this setting, LTM does not resume SSL sessions after an unclean shutdown.

About session tickets

To enhance system performance, you can enable the use of session tickets, a TLS extension defined in RFC 5077. The use of session tickets is an alternative to the standard session caching mechanism that systems such as the BIG-IP system typically use to resume sessions.

When you enable this feature, the BIG-IP system, acting as a server to terminate SSL connections, sends a special message to the client as part of the SSL handshake. This message includes a session ticket, which contains complete session state information. Sending the session state information to the client removes the need for the BIG-IP system to maintain a server-side cache for storing session information. With session tickets, the entire session state is remembered by the client.

The session state information in the ticket includes the master secret negotiated between the client and the BIG-IP system, as well as the cipher suite used.

Generic alerts

For security reasons, when sending an SSL alert message, the BIG-IP® system sends a generic handshake failure message with an alert code of 40, with no detailed information. This is the default behavior.

If you want SSL alert messages to include the specific reason for the failure, you can disable the Generic Alerts setting. In this case, when an SSL failure occurs, the system sends an alert message with a specific numeric code. For example, an alert message due to a certificate revocation would show a specific code of 48 instead of the generic code of 40.

Acceptance of non-SSL connections

You can configure Local Traffic Manager™ to accept connections that are not SSL connections. In this case, connections pass through the BIG-IP® system in clear-text format. By default, this setting is disabled.

SSL sign hash

You can specify the specific hash algorithm that you want the BIG-IP® system to use for server key exchange with Elliptic Curve ciphers. Possible choices are SHA1, SHA256, SHA384, or Any. When you select Any, you authorize the system to choose any one of the hash algorithms. Note that in this case, the BIG-IP system chooses SHA1 whenever possible.

Table of Contents   |   << Previous Chapter   |   Next Chapter >>

Was this resource helpful in solving your issue?




NOTE: Please do not provide personal information.



Incorrect answer. Please try again: Please enter the words to the right: Please enter the numbers you hear:

Additional Comments (optional)