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The DROWN Attack In Focus

Posted on 3.02.2016

Security researchers have identified a new method for deciphering the contents of (supposedly) secure communications.

The DROWN attack, is a cross-protocol attack that affects HTTPS and other services that rely on SSL and TLS, some of the essential cryptographic protocols for Internet security. This could prove to be a major problem as these protocols allow everyone on the Internet to browse the web, use email, shop online, and other digital activities without third-parties being able to read the communication. Websites, mail servers, and other TLS-dependent services are at risk for the DROWN attack, and many popular sites including Yahoo, BuzzFeed, Groupon and others are currently affected.

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Most modern servers and clients use the TLS encryption protocol, but due to misconfigurations, many servers also still support SSLv2, a 1990s-era predecessor to TLS. This support did not matter in practice, since no up-to-date clients actually use SSLv2. Therefore, even though SSLv2 is known to be badly insecure, until now, merely supporting SSLv2 was not considered a security problem, because clients never used it.

DROWN shows that merely supporting SSLv2 is a threat to modern servers and clients as it allows an attacker to decrypt modern TLS connections between up-to-date clients and servers by sending probes to a server that supports SSLv2 and uses the same private key.

To protect against DROWN, server operators need to ensure that their private keys are not used anywhere with server software that allows SSLv2 connections. This includes web servers, SMTP servers, IMAP and POP servers, and any other software that supports SSL/TLS. You can use the form above to check whether your server appears to be exposed to the attack.

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