"... it not be shown."
This is a form of the subjunctive licensed by the preposition phrase on (the) condition. Many nouns, such as the noun condition can take content clauses using subjunctive constructions. Usually these clauses indicate the desired outcome of some implicit or explicit command or instruction.
Here are some more examples of the subjunctive following the noun condition from printed books. Notice that the verbs are in the plain form. They do not exhibit the third person 'S' that we would expect if these were examples of present simple verb forms:
Calkins, a young Greek and philosophy instructor at Wellesley College, was given the opportunity to establish a laboratory on the condition that she take time off and pursue advanced studies in psychology.
She was discharged by the Postal Service but later reinstated on the condition that she take her medication.
She was granted permission — on the condition that she take the exam apart from the male students.
When head of the verb phrase in the content clause is the verb BE, the use of the subjunctive is more striking, of course, because the plain form of the verb BE, namely be, looks and sounds very different from the present simple forms am, is or are:
- A radio station eventually arranged to spend the night in the room, which Bruhns allowed only on the condition that she be there to ensure security.
The Original Poster's example
- CNN viewed the email on the condition that [it not be shown].
Here we see a content clause using a subjunctive construction. The corresponding present simple version of the clause would be:
- it is not shown.
In the OP's (Original Poster's) example, we see the passive auxiliary BE, which heads the verb phrase, in the plain form. Because this is a subjunctive construction, the clause is negated by the word not occurring before instead of after this verb. It is a perfectly grammatically correct sentence.
Speakers of British English are less likely to use subjunctive constructions than American English speakers.