A simple explanation of a backdoor
Irshaad Abdool contacted hackers.mu concerning the Juniper vulnerability here Unfortunately, reverse engineering a firmware image, and explaining assembly code doesn't cut it for a lot of the young IT folks :)
The vulnerability
A strcmp() call was inserted. strcmp() is used for string comparisons. If it's successful, you can proceed, if Not, you are denied. In this particular case, this was inserted right before the normal authentication with SSH (or telnet). So you had your normal login, that went through the normal SSH (and telnet) code, but right before that, you had a special user that could login, and bypass the normal SSH and telnet login. That's in summary how this vulnerability works.
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