We present DROWN, a novel cross-protocol attack on TLS that uses a server supporting SSLv2 as an oracle to decrypt modern TLS connections.
We introduce two versions of the attack. The more general form exploits multiple unnoticed protocol flaws in SSLv2 to develop a new and stronger variant of the Bleichenbacher RSA padding-oracle attack. To decrypt a 2048-bit RSA TLS ciphertext, an attacker must observe
1,000 TLS handshakes, initiate 40,000 SSLv2 connections, and perform 2^50 offline work. The victim client never initiates SSLv2 connections. We implemented the attack and can decrypt a TLS 1.2 handshake using 2048-bit RSA in under 8 hours, at a cost of $440 on Amazon EC2. Using Internet-wide scans, we find that 33% of all HTTPS servers and 22% of those with browser-trusted certificates are vulnerable to this protocol-level attack due
to widespread key and certificate reuse.
For an even cheaper attack, we apply our new techniques together with a newly discovered vulnerability in OpenSSL that was present in releases from 1998 to early 2015. Given an unpatched SSLv2 server to use as an oracle, we can decrypt a TLS ciphertext in one minute on a single CPU - fast enough to enable man-in-the-middle attacks against modern browsers. We find that 26% of HTTPS servers are vulnerable to this attack.
We further observe that the QUIC protocol is vulnerable to a variant of our attack that allows an attacker to impersonate a server indefinitely after performing as few as 2^17 SSLv2 connections and 2^58 offline work.
We conclude that SSLv2 is not only weak, but actively harmful to the TLS ecosystem.
For decades, the Network Time Protocol (NTP) has been used to synchronize computer clocks over untrusted network paths. This work takes a new look at the security of NTP’s datagram protocol. We argue that NTP’s datagram protocol in RFC5905 is both underspecified and flawed. The NTP specifications do not sufficiently respect (1) the conflicting security requirements of different NTP modes, and (2) the mechanism NTP uses to prevent off-path attacks. A further problem is that (3) NTP’s control-query interface reveals sensitive information that can be exploited in off-path attacks. We exploit these problems in several attacks that remote attackers can use to maliciously alter a target’s time. We use network scans to find millions of IPs that are vulnerable to our attacks. Finally, we move beyond identifying attacks by developing a cryptographic model and using it to prove the security of a new backwards-compatible client/server protocol for NTP.