Require a minimum SASL security factor of 56

SSF_MINX 56 level ensures data integrity and confidentiality for SASL
GSSAPI and SASL GSS SPNEGO connections.

Although at least AES128 is enforced pretty much everywhere, 56 is required
for backwards compatibility with systems that announce wrong SSF.

Related: https://pagure.io/freeipa/issue/7140
Related: https://pagure.io/freeipa/issue/4580
Signed-off-by: Christian Heimes <cheimes@redhat.com>
Reviewed-By: Rob Crittenden <rcritten@redhat.com>
Reviewed-By: Tibor Dudlak <tdudlak@redhat.com>

install/share/Makefile.am

@@ -94,6 +94,7 @@ dist_app_DATA =				\
 	ipa-kdc-proxy.conf.template	\
 	ipa-pki-proxy.conf.template	\
 	ipa-rewrite.conf.template	\
+	min-ssf.ldif			\
 	$(NULL)
 
 kdcproxyconfdir = $(IPA_SYSCONF_DIR)/kdcproxy

install/share/min-ssf.ldif

@@ -0,0 +1,14 @@
+# config
+# pretend SSF for LDAPI connections
+# nsslapd-localssf must be equal to or greater than nsslapd-minssf
+dn: cn=config
+changetype: modify
+replace: nsslapd-localssf
+nsslapd-localssf: 256
+
+# minimum security strength factor for SASL and TLS
+# 56 is considered weak, but some old clients announce wrong SSF.
+dn: cn=config
+changetype: modify
+replace: nsslapd-minssf
+nsslapd-minssf: 56

ipalib/constants.py

@@ -309,6 +309,9 @@ TLS_VERSIONS = [
 ]
 TLS_VERSION_MINIMAL = "tls1.0"
 
+# minimum SASL secure strength factor for LDAP connections
+# 56 provides backwards compatibility with old libraries.
+LDAP_SSF_MIN_THRESHOLD = 56
 
 # Use cache path
 USER_CACHE_PATH = (

ipapython/ipaldap.py

@@ -43,7 +43,9 @@ import six
 
 # pylint: disable=ipa-forbidden-import
 from ipalib import errors, x509, _
-from ipalib.constants import LDAP_GENERALIZED_TIME_FORMAT
+from ipalib.constants import (
+    LDAP_GENERALIZED_TIME_FORMAT, LDAP_SSF_MIN_THRESHOLD
+)
 # pylint: enable=ipa-forbidden-import
 from ipaplatform.paths import paths
 from ipapython.ipautil import format_netloc, CIDict
@@ -103,7 +105,8 @@ def realm_to_ldapi_uri(realm_name):
     return 'ldapi://' + ldapurl.ldapUrlEscape(socketname)
 
 
-def ldap_initialize(uri, cacertfile=None):
+def ldap_initialize(uri, cacertfile=None,
+                    ssf_min_threshold=LDAP_SSF_MIN_THRESHOLD):
     """Wrapper around ldap.initialize()
 
     The function undoes global and local ldap.conf settings that may cause
@@ -114,6 +117,10 @@ def ldap_initialize(uri, cacertfile=None):
       locations, also known as system-wide trust store.
     * Cert validation is enforced.
     * SSLv2 and SSLv3 are disabled.
+    * Require a minimum SASL security factor of 56. That level ensures
+      data integrity and confidentiality. Although at least AES128 is
+      enforced pretty much everywhere, 56 is required for backwards
+      compatibility with systems that announce wrong SSF.
     """
     conn = ldap.initialize(uri)
 
@@ -121,6 +128,12 @@ def ldap_initialize(uri, cacertfile=None):
     conn.set_option(ldap.OPT_X_SASL_NOCANON, ldap.OPT_ON)
 
     if not uri.startswith('ldapi://'):
+        # require a minimum SSF for TCP connections, but don't lower SSF_MIN
+        # if the current value is already larger.
+        cur_min_ssf = conn.get_option(ldap.OPT_X_SASL_SSF_MIN)
+        if cur_min_ssf < ssf_min_threshold:
+            conn.set_option(ldap.OPT_X_SASL_SSF_MIN, ssf_min_threshold)
+
         if cacertfile:
             if not os.path.isfile(cacertfile):
                 raise IOError(errno.ENOENT, cacertfile)

ipaserver/install/dsinstance.py

@@ -324,6 +324,8 @@ class DsInstance(service.Service):
         else:
             self.step("importing CA certificates from LDAP",
                       self.__import_ca_certs)
+        # set min SSF after DS is configured for TLS
+        self.step("require minimal SSF", self.__min_ssf)
         self.step("restarting directory server", self.__restart_instance)
 
         self.start_creation()
@@ -1241,6 +1243,9 @@ class DsInstance(service.Service):
             dm_password=self.dm_password
         )
 
+    def __min_ssf(self):
+        self._ldap_mod("min-ssf.ldif")
+
     def __add_sudo_binduser(self):
         self._ldap_mod("sudobind.ldif", self.sub_dict)