By Dan Goodin
19th May 2009
Cryptographers are urging users of a widely employed network protocol to
make sure they're running the latest version after discovering a flaw
that could allow attackers to read data that's supposed to remain
All programs that incorporate the OpenSSH implementation of SSH, short
for Secure Shell, should make sure they use version 5.2, which provides
several countermeasures to prevent the attacks. Other SSH
implementations may be vulnerable as well, the researchers from the
Information Security Group at the University of London's Royal Holloway
The attack exploits subtle differences in the way SSH software reacts
when encountering errors during cryptographic processing. By directing
specially manipulated packets at the application, an attacker has a one
in 262,144 chance of recovering 32 bits of plaintext from an arbitrary
chunk of ciphertext.
While those are extremely limited odds, the design flaw still poses a
significant threat given the way many applications that employ SSH work.
VPNs, or virtual private networks, for example, repeatedly reconnect to
a server extremely rapidly each time they are disconnected. With some
programs reconnecting several times per second, a determined attacker
might find ample opportunity to succeed.
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