OpenSSL patches critical LogJam TLS flaw

The OpenSSL Project yesterday issued seven software patches in a security advisory which addresses the critical 'LogJam' vulnerability (CVE-2015-4000) in the TLS protocol.

Discovered last month by various security researchers, LogJam potentially allowed Man-in-the-Middle (MiTM) attackers to downgrade vulnerable TLS connections using the DHE key exchange algorithm to 512-bits to crack the connection and view its contents.

LogJam, which has been compared to the Freak flaw although it relates to a vulnerability in TLS rather than implementation flaw, was said to have affected 80,000 of world's most popular HTTPS websites, although it's not believed there were many, if any, successful in-the-wild attacks. All modern web browsers were affected, and experts said nation-states could have looked to exploit the flaw.

OpenSSL 1.0.2 users are now encouraged to upgrade to 1.0.2b, with 1.0.1 users urged to upgrade to 1.0.1n. Doing so will make their clients and servers safe from LogJam attacks in future, as OpenSSL says that these patches will reject encryption handshakes with DH parameters shorter than 768 bits. In future, the group hopes to increase that limit to 1,024 bits.

Of the other fixes, five were rated as ‘moderate' and one as ‘low' severity. Most would allow a denial-of-service attack against a vulnerable system, while one could lead to a memory corruption attack.

OpenSSL, which is arguably the world's most important web security library with its support for Secure Sockets Layer (SSL) and Transport Layer Security (TLS), has also reminded users that support for OpenSSL versions 1.0.0 and 0.9.8 will end on 31 December. This means that there will be no security updates for these releases after that date.

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