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: 102479-12: SunOS 5.4: libresolv, in.named, named-xfer, nslookup ... 102480-10: SunOS 5.4_x86: libresolv, in.named, named-xfer, nslookup ...