mirror of
https://github.com/carlospolop/hacktricks
synced 2024-12-20 18:14:15 +00:00
44 lines
2.2 KiB
Markdown
44 lines
2.2 KiB
Markdown
# IDS and IPS Evasion
|
|
|
|
## **TTL Manipulation**
|
|
|
|
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.
|
|
|
|
**Nmap option:** `--ttlvalue <value>`
|
|
|
|
## Avoiding signatures
|
|
|
|
Just add garbage data to the packets so the IPS/IDS signature is avoided.
|
|
|
|
**Nmap option:** `--data-length 25`
|
|
|
|
## **Fragmented Packets**
|
|
|
|
Just fragment the packets and send them. If the IDS/IPS doesn't have the ability to reassemble them, they will arrive to the final host.
|
|
|
|
**Nmap option:** `-f`
|
|
|
|
## **Invalid** _**checksum**_
|
|
|
|
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.
|
|
|
|
## **Uncommon IP and TCP options**
|
|
|
|
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.
|
|
|
|
## **Overlapping**
|
|
|
|
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.
|
|
Or maybe, 2 packets with the same offset comes and the host has to decide which one it takes.
|
|
|
|
* **BSD**: It has preference for packets with smaller _offset_. For packets with same offset, it will choose the first one.
|
|
* **Linux**: Like BSD, but it prefers the last packet with the same offset.
|
|
* **First** \(Windows\): First value that comes, value that stays.
|
|
* **Last** \(cisco\): Last value that comes, value that stays.
|
|
|
|
## Tools
|
|
|
|
* [https://github.com/vecna/sniffjoke](https://github.com/vecna/sniffjoke)
|
|
|