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Send some packets with a TTL enough to arrive to the IDS/IPS but not enough to arrive to the final system. And then, send another packets with the same sequences as the other ones so the IPS/IDS will think that they are repetitions and won't check them, but indeed they are carrying the malicious content.
Sensors usually don't calculate checksum for performance reasons. __ So an attacker can send a packet that will be **interpreted by the sensor but rejected by the final host.** Example:
Send a packet with the flag RST and a invalid checksum, so then, the IPS/IDS may thing that this packet is going to close the connection, but the final host will discard the packet as the checksum is invalid.
A sensor might disregard packets with certain flags and options set within IP and TCP headers, whereas the destination host accepts the packet upon receipt.
It is possible that when you fragment a packet, some kind of overlapping exists between packets (maybe first 8 bytes of packet 2 overlaps with last 8 bytes of packet 1, and 8 last bytes of packet 2 overlaps with first 8 bytes of packet 3). Then, if the IDS/IPS reassembles them in a different way than the final host, a different packet will be interpreted.\
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- **Share your hacking tricks by submitting PRs to the [hacktricks repo](https://github.com/carlospolop/hacktricks) and [hacktricks-cloud repo](https://github.com/carlospolop/hacktricks-cloud)**.
