During a penetration test, you have already sniffed a victim's TCP session cookie on a corporate LAN and plan to inject your own data into the stream to capture credentials. Before sending the forged packets, you want to minimize the chance that the network's signature- and anomaly-based IDS will detect the hijacking attempt. Which technique provides the most reliable method of evading the IDS while still allowing the victim's TCP stack to accept your injected data?
Throttle the TCP window size field to the minimum to exhaust the IDS's session table and make it drop tracking state.
Launch an ARP cache-poisoning attack first, hoping the IDS will ignore traffic that appears to stay on the local segment.
Split the malicious payload into multiple small TCP segments with overlapping sequence numbers so only the target host-not the IDS-reassembles the altered bytes.
Spoof the packet's source IP and use varying TTL values to force asymmetric routing around the IDS sensor.
Intentionally fragmenting or segmenting the injected payload so it arrives as multiple, small TCP segments with carefully chosen, overlapping sequence numbers is a classic IDS-evasion tactic. Many intrusion detection engines either reassemble only the first instance of overlapping data or give precedence to the first-seen bytes, while most modern operating-system TCP stacks accept the last-seen bytes when overlaps occur. By positioning the malicious portion of the payload in the later, overlapping segment, the attacker ensures the IDS inspects a benign stream, yet the victim host reassembles and processes the altered data, allowing the session hijack to proceed undetected.
Sending traffic through ARP poisoning does not of itself hide packet contents from the IDS, IP-TTL spoofing can help slip past some routers but modern IDSs analyze both directions of a flow, and lowering the TCP window size is more likely to disrupt the connection than evade detection. Therefore, controlled overlapping TCP segmentation is the most effective choice for this scenario.
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