Cambridge

Dear Sagar,
You must visit the respective university websites for program specific requirements and criteria. You have not mentioned the program you are seeking entry to. Hence, I would urge you to check the details on the webpages directly.
Significance of class 12th may be debatable. First, without a formal and sound foundation you cannot compete in the international education scenario. Second, the universities in question are world's top most and ensures high quality of education in terms of career outcomes, research etc. Therefore they select and admit only the best through a rigorous selection process and thus maintaining their world-class standard.

Cambridge MBA eligibility:
Professional experience:
3 years full-time work experience after completion of your undergraduate degree
English proficiency
English as your native language
or TOEFL - 110, with no element below 25
or IELTS - 7.5, with no element below 7.0
Undergraduate academic achievement
1st or 2.1
or GPA of at least 3.3
or Top 25% of class
GMAT
Current class average - 690
Mid 80% - (640-740)
A balanced score is required
Valid GRE scores also accepted
source: University of Cambridge Judge Bschool website
University of Oxford MBA
GMAT: score of 650 or above. current class has an average GMAT score of around 690
GRE: GRE verbal score of 160 and a quantitative score of 161.
TOEFL
Minimum Score 110
Minimum required on each component:
Listening - 22
Reading - 24
Writing - 24
Speaking - 25
IELTS
7.5
minimum required on each component
7.0
source: University of Oxford website
Please go through the respective University website for detailed eligibility.