As you might have heard there is a flaw in many popular email clients that allows an attacker to decrypt PGP or S/MIME encrypted email content.
Here's the website with all of the info about the attacks: EFAIL
Let's collect mitigation techniques especially for the clients affected by the direct exfiltration attack (Apple Mail, iOS Mail, and Mozilla Thunderbird)
Some immediate mitigations I've read about so far:
- Turn off OpenPGP and S/MIME encryption in your mail client and use an external tool (eg. Keybase) for encryption/decryption by copy-pasting content.
- Disable HTML support. Only show plaintext
- (For Thunderbird) Leave OpenPGP encryption enabled but turn off automatic decryption/verification of messages in Enigmail settings
- (For Thunderbird) Disallow remote content in messages.
The last 2 just protect you from stumbling into the attack. You can still be exploited if you accept remote content for that particular mail and/or if you manually decrypt the message.