GEN:SID 1:1394
Message SHELLCODE x86 NOOP
Summary This event is generated when an attempt is made to possibly overflow a buffer.

The NOOP warning occurs when a series of NOOP (no operation) are found in a stream. Most buffer overflow exploits typically use NOOPs sleds to pad the code.
Impact This might indicate someone is trying to use a buffer overflow exploit.

Full compromise of  system is possible if the exploit is successful.
Detailed Information This rule detects a large number of consecutive NOOP instructions used in padding code. It's not specific to a particular service exploit, but rather used to try and detect buffer overflows in general. It is common for buffer overflow code to contain a large sequence of NOOP instructions as it increases the odds of successful execution of the useful shellcode.
Affected Systems Any x86 programs.
Attack Scenarios An attacker uses a buffer overflow exploit which contains the following payload:

    90 90 90 90 90 90 90 90 90 90 /bin/sh
Ease of Attack Simple.
Corrective Action Apply a non-executable user stack patch to your kernel

Secure programming/execution of a program

Check the destination host and service to verify if any buffer overflow vulnerability exists.
Additional References