Critical vulnerabilities in PGP/GPG and S/MIME email encryption, warn researchers

Critical vulnerabilities in PGP/GPG and S/MIME email encryption, warn researchers

Critical vulnerabilities in PGP/GPG and S/MIME email encryption, warn researchers

While encrypted email keeps your messages secret, email clients see HTML content - for example, images or hyperlinks - and translate them in plain-text, even if there is encrypted content in them.

The Electronic Frontier Foundation recommends that people "immediately disable and/or uninstall tools that automatically decrypt PGP-encrypted email".

"If you use PG or S/MIME for sensitive information then this is a big deal", Matt Green, a professor specializing in encryption at Johns Hopkins University, told Ars on Monday. The EFF's report only indicated that a vulnerability existed, and that users should disable PGP plugins in their mail clients until patches are deployed.

The new critical vulnerability is dubbed as EFAIL, and the researchers say that there is no permanent fix available now.

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This turning into another Heartbleed is unlikely given that this level of encryption is, for most, belt and braces - nobody cares what you had for dinner - but for those who rely on PGP for genuine confidentiality?

The Gnu Privacy Guard (GnuPG) team responded to the EFF's warnings by saying the problem lies with how email clients implement OpenPGP, not with the protocol itself. Users can employ PGP-compatible email clients themselves, and many secure webmail clients also make use of PGP.

A group of nine researchers has discovered a critical vulnerability in the systems end-to-end email encryption using OpenPGP and S/MIME. The organization provided step-by-step guides explaining how to do just that in Apple Mail, Outlook, and Thunderbird, which are the most popular clients affected by EFAIL. In computer security, an oracle attack refers to an attackers being able to exploit a vulnerability to extract information from a target. In one attack method, the researchers take advantage of Cipher Feedback Mode (CFB) in OpenPGP and Cipher Block Chaining (CBC) in S/MIME. "Or if you really need to read them use a proper MIME parser and disallow any access to external links", he says. In a post Monday, he said his team wasn't contacted about the flaw and the attack could be mitigated by avoiding HTML emails or using authenticated encryption, which adds a layer of protection to confirm the message hasn't been changed. CounterMail, Hushmail and Mailfence all use OpenPGP.

UPDATE 2: Because some researchers started disclosing details about the vulnerability ahead of schedule, the efail.de website is now live, along with the research paper, both containing more info on the EFAIL vulnerability. And many corporate email services employ S/MIME.

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