(credit: Koichi Taniguchi)

The Mac keychain is a digital vault of sorts that stores passwords and cryptographic keys. Apple engineers have designed it so that installed applications can’t access its contents without the user entering a master password. A weakness in the keychain, however, allows rogue apps to steal every plaintext password it stores with no password required. Patrick Wardle, a former National Security Agency hacker who now works for security firm Synack, posted a video demonstration here.

The video shows a Mac virtual machine running High Sierra as it installs an app. Once the app is installed, the video shows an attacker on a remote server running the Netcat networking utility. When the attacker clicks “exfil keychain” button, the app surreptitiously exfiltrates all the passwords stored in the keychain and uploads them to the server. The theft requires no user interaction beyond the initial installation of the rogue app, and neither the app nor macOS provides any warning or seeks permission.