INFLT WX ENCOUNTER. DSNDING OUT OF CLOUD LAYER; FLC HIT SMALL CUMULO NIMBUS AND TURB WHICH RESULTED IN 4 FLT ATTENDANTS BEING INJURED.

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INBOUND TO ATLANTA FROM FRANKFURT GERMANY; WE WERE CLRED TO 14000 FT ON THE MACEY ARR. THERE WAS A CLOUD LAYER AHEAD THAT WE COULD SEE WAS CLR BENEATH AND A FEW SMALL CUMULO NIMBUS WELL S OF THE ARR RTE. 14000 FT PUT US IN THIS CLOUD LAYER AND I REQUESTED A LOWER ALT TO GET BENEATH IT INTO THE CLR AND A SMOOTHER RIDE (LIGHT CHOP IN CLOUDS). WE WERE CLRED TO 12000 FT. THE BASE OF THIS LAYER WAS ABOUT 12500 FT TO 13000 FT; AND AS WE CAME THROUGH THIS; WE WERE FACE TO FACE WITH A VERY SMALL CUMULO NIMBUS; NOT MUCH WIDER THAN MY WINGSPAN AND TOPS ABOUT 12500 FT. TOO LATE TO AVOID. WE ENCOUNTERED TWO MODERATE JOLTS AS WE PASSED THROUGH THIS THEN INTO THE CLR AND SMOOTH AIR AGAIN. THERE WAS NO PRECIPITATION ASSOCIATED WITH THIS AS WE PASSED THROUGH IT AND THERE WERE NO RADAR RETURNS ANYWHERE NEAR OUR RTE. THE SEAT BELT SIGN HAD BEEN ON SINCE ABOUT FL250 SO THE FLT ATTENDANTS COULD SECURE THE CABIN FOR LNDG. UNFORTUNATELY; 4 OF THE 13 FLT ATTENDANTS (THE 4 WHO WERE IN OR NEAR THE AFT GALLEY) SUSTAINED SOME MINOR INJURIES. ALERTED MY COMPANY AND HAD MEDICAL ASSISTANCE MEET US UPON ARR.