OA68554: ALLOW GSK_CERT_VALIDATION_MODE SETTING TO BE USED WHEN CHECKING THE LOCAL CERTIFICATE EXTENDED KEY USAGE IN A TLS1.3 ENVIRONMENT

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• Currently, System SSL checks that if the local certificate has
  an extended key usage (EKU) it must be appropriate for its
  intended usage. This means that for server applications the EKU
  must specify serverAuth or anyExtendedKeyUsage. While for client
  
  applications, this means that the EKU must specify clientAuth or
  
  anyExtendedKeyUsage. In TLS 1.3, this is always done by default
  without regard to the GSK_CERT_VALIDATION_MODE setting. TLS 1.3
  defaults to RFC 5280. The GSK_CERT_VALIDATION_MODE setting
  should be examined prior to these checks.  In these cases, the
  TLS handshake would fail with return code 440 from the
  gsk_secure_socket_init() API.
  
  Additionally, when we validate the peer's certificate we should
  also take into account the GSK_CERT_VALIDATION_MODE setting when
  
  examining the EKU during TLS 1.3 handshakes.
  

Local fix

Problem summary

• ****************************************************************
  * USERS AFFECTED: System SSL applications that are performing  *
  *                 TLS V1.3 handshakes with certificates        *
  *                 containing an extended key usage (EKU)       *
  *                 extension.                                   *
  ****************************************************************
  * PROBLEM DESCRIPTION: When performing a TLS V1.3 handshake    *
  *                      with a certificate containing an EKU    *
  *                      extension, System SSL verifies that the *
  *                      local certificate is valid for its      *
  *                      intended purpose to follow RFC 5280     *
  *                      certificate validation rules. If the    *
  *                      local certificate is not valid for the  *
  *                      intended purpose, the                   *
  *                      gsk_secure_socket_init() fails the TLS  *
  *                      V1.3 handshake with return code 440.    *
  ****************************************************************
  * RECOMMENDATION: APPLY PTF                                    *
  ****************************************************************
  Within a TLS V1.3 handshake, the local certificate's EKU
  extension check is performed unconditionally without examining
  the GSK_CERT_VALIDATION_MODE setting. By default, System SSL
  uses RFC 5280 certificate validation mode which checks the
  extended key usage extension for its intended purpose.
  Similarly, when System SSL receives a certificate from a partner
  containing an EKU extension, it always performs the check
  unconditionally without querying the GSK_CERT_VALIDATION_MODE
  setting during TLS V1.3 handshakes.
  

Problem conclusion

• The code was updated to query the GSK_CERT_VALIDATION_MODE
  setting when attempting a TLS V1.3 handshake and the local or
  the partner's certificate contains an extended key usage
  extension. If the EKU checks need to be bypassed, the
  GSK_CERT_VALIDATION_MODE setting can be set to 2459. If the
  GSK_CERT_VALIDATION_MODE setting is 3280 or 5280, the
  certificate EKU checks are performed.
  
  The z/OS Cryptographic Services System Secure Sockets Layer
  Programming publication (SC14-7495) has been updated. For the
  specific topics that were updated, see the "Summary of Changes"
  section of the publication related to z/OS 3.2.
  

Temporary fix

Comments

APAR Information

• APAR is sysrouted FROM one or more of the following:

• APAR is sysrouted TO one or more of the following:

  UJ98631 UJ98632 UJ98633 UJ98634 UJ98635 UJ98636

Modules/Macros

• GSKCMS31 GSKCMS64 GSKS31   GSKS31F  GSKS64   GSKS64F
  

Fix information

• Fixed component name

  SYSTEM SSL

• Fixed component ID

  565506805

Applicable component levels

• R450 PSY UJ98635

     UP25/12/13 P F512

• R451 PSY UJ98636

     UP25/12/13 P F512

• R510 PSY UJ98633

     UP25/12/13 P F512

• R511 PSY UJ98634

     UP25/12/13 P F512

• R520 PSY UJ98631

     UP25/12/13 P F512

• R521 PSY UJ98632

     UP25/12/13 P F512

Fix is available

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