That's caused by a bug in the Solaris 2.4 named. You need to install the appropriate one of the following patches: 102479-01: SunOS 5.4: memory leak/mismanagement in in.named 102480-01: SunOS 5.4_x86: memory leak/mismanagement in in.named
The latest version of these patches include bind 4.9.3: 102479-02: SunOS 5.4: DNS spoofing is possible per Cern ca-96.02 102480-02: SunOS 5.4_x86: DNS spoofing is possible per Cern ca-96.02