During WWII, there were a number of War Department Circulars that identified circumstances required to meet in order to be eligible for the CIB.
The initial WD Circular was 269, dated 27 October 1943.
3. Combat Infantry Badge.—Infantrymen, including officers, establish eligibility to wear the Combat Infantryman Badge by— a. Exemplary conduct in action against the enemy, or b. By satisfactory performance of duty in action against the enemy in a major operation as determined and announced by the theater commander.
Please note the MOS of an infantryman was not required (by my research) not until 1961.
History reveals hundreds of combat infantrymen without the MOS fought in the Battle of Bataan, and Battle of the Bulge were awarded the CIB.
For example: In the PTO: Members of tank units Member of AAA automatic weapons unit AAF personnel
In the ETO: A member of a tank unit Members of the 7th AD A member of the 106th ID with MOS of a photographer A member of the 106th ID with MOS of a truck driver, light AAF personnel Members of a combat engineer unit
Regardless the MOS, the individual fought in the Battle of the Aleutian Islands as an infantryman, he is entitled to the CIB.
Please note:All recipients of the CIB during WWII are entitled to the Bronze Star Medal.