Low-cost DROWN attack decrypts data in hours, works against TLS e-mail servers, too.
by Dan Goodin
More than 11 million websites and e-mail services protected by the transport layer security protocol are vulnerable to a newly discovered, low-cost attack that decrypts sensitive communications in a matter of hours and in some cases almost immediately, an international team of researchers warned Tuesday. More than 81,000 of the top 1 million most popular Web properties are among the vulnerable HTTPS-protected sites.
The attack works against TLS-protected communications that rely on the RSA cryptosystem when the key is exposed even indirectly through SSLv2, a TLS precursor that was retired almost two decades ago because of crippling weaknesses. The vulnerability allows an attacker to decrypt an intercepted TLS connection by repeatedly using SSLv2 to make connections to a server. In the process, the attacker learns a few bits of information about the encryption key each time. While many security experts believed the removal of SSLv2 support from browser and e-mail clients prevented abuse of the legacy protocol, some misconfigured TLS implementations still tacitly support the legacy protocol when an end-user computer specifically requests its use. The most notable implementation subject to such fatal misconfigurations is the OpenSSL cryptographic library, which on Tuesday is expected to release an update that makes such settings much less likely to occur.
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