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Next: Configuration Up: Preprocessors Previous: Examples/Default Configuration from snort.conf   Contents


SSH

The SSH preprocessor detects the following exploits: Gobbles, CRC 32, Secure CRT, and the Protocol Mismatch exploit.

Both Gobbles and CRC 32 attacks occur after the key exchange, and are therefore encrypted. Both attacks involve sending a large payload (20kb+) to the server immediately after the authentication challenge. To detect the attacks, the SSH preprocessor counts the number of bytes transmitted to the server. If those bytes exceed a pre-defined limit within a pre-define number of packets, an alert is generated. Since Gobbles only effects SSHv2 and CRC 32 only effects SSHv1, the SSH version string exchange is used to distinguish the attacks.

The Secure CRT and protocol mismatch exploits are observable before the key exchange.


Subsections
Steven Sturges 2006-12-08
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