Blabbermouth (noun)

A person who talks too much or reveals secrets, often in a indiscreet or thoughtless manner.

Origin:

From blabber + mouth.

Examples:

1. He is such a blabbermouth, he can't keep a secret.
2. She is known for being a blabbermouth, always gossiping.
3. The blabbermouth revealed the secret to her friends.
4. He blabbermouthed the company's confidential information.
5. The blabbermouth caused a lot of trouble by revealing the secret.