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The four-way handshake is designed so that the access point (or authenticator) and wireless client (or supplicant) can independently prove to each other that they know the PSK/PMK, without ever disclosing the key.
For connections using AES and the Counter with CBC-MAC Protocol ((AES)-CCMP), an attacker can decrypt network packets, making it possible to read their contents and to inject malicious content into TCP packet streams. But the key itself cannot be broken or forged, so the attacker can't forge a key and join the network—instead, they have to use a "cloned" access point that uses the same MAC address as the access point of the targeted network, on a different Wi-Fi channel.For WPA2 systems using the Temporal Key Integrity Protocol (TKIP), the Message Integrity Code key can be recovered by the attacker. This allows them to replay captured packets to the network; they can also forge and transmit new packets to the targeted client posing as the access point.For devices that use the Galois/Counter Mode Protocol (GCMP), the attack is the worst: "It is possible to replay and decrypt packets," Vanhoef and Piessens wrote. "Additionally, it is possible to recover the authentication key, which in GCMP is used to protect both communication directions [as client or access point]… therefore, unlike with TKIP, an adversary can forge packets in both directions." That means that the attacker can essentially join the network and pretend to be a client or the access point, depending on the type of access they want. "Given that GCMP is expected to be adopted at a high rate in the next few years under the WiGig name, this is a worrying situation," the researchers noted.
Our advice, which mirrors that of the researchers, is to immediately disable and/or uninstall tools that automatically decrypt PGP-encrypted email. Until the flaws described in the paper are more widely understood and fixed, users should arrange for the use of alternative end-to-end secure channels, such as Signal (Android, iOS), and temporarily stop sending and especially reading PGP-encrypted email.
The EFAIL attacks exploit vulnerabilities in the OpenPGP and S/MIME standards to reveal the plaintext of encrypted emails. In a nutshell, EFAIL abuses active content of HTML emails, for example externally loaded images or styles, to exfiltrate plaintext through requested URLs. To create these exfiltration channels, the attacker first needs access to the encrypted emails, for example, by eavesdropping on network traffic, compromising email accounts, email servers, backup systems or client computers. The emails could even have been collected years ago.
Attack scenario.In our model, the attacker is able to collect end-to-end encrypted emails, either through a man-in-the-middle attack on the network, by accessing a SMTP server, by accessing the IMAP account on the server, or by some other means. He may store these emails for some time before he starts his attack. To decrypt the emails, he first manipulates their ci phertext by using appropriate malleability gadgets. In order to make these manipulations work, he may make informed guesses about the operating system, the email client and the encryption software the victim uses. He then sends the manipulated email to one of the original receivers, or to the original sender. He may hide this by choosing new FROM, DATE and SUBJECT fields, and he may hide the manipulated ciphertext by hiding it within an invisible iFrame. Thus the attack mail the victim receives looks unsuspicious.Once he opens the email in his client, the manipulated ciphertext will be decrypted – first the private key of the victim is used to decrypt the session keys, and then this session key is used to decrypt the manipulated ciphertext c. The decrypted plaintext now contains, due to the manipulations, an exfiltration channel (e.g., an HTML hyperlink) that will send the decrypted plaintext as a whole or in parts to the attacker.
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Subiect: Cum va protejati computerul? (Citit de 12873 ori)
