answer:When TCP timestamps are enabled (specified by the TCP Timestamps Option (TSopt) as per RFC 7323), an attacker who wants to successfully implement an attack with a forged RST packet must correctly guess or know not just the sequence number, but also the timestamp value expected by the receiving host. TCP timestamps serve two main purposes: 1. **PAWS (Protection Against Wrapped Sequence numbers):** This is primarily to protect against old duplicate segments disrupting the current connection when the sequence number space wraps around. 2. **RTT Measurement:** It helps in measuring the round-trip time (RTT) more accurately, aiding in overall TCP performance. For the attack to be successful, the bogus RST packet must have: - A sequence number within the receiver's window. - A TCP timestamp value that is equal to or greater than the last timestamp received from the legitimate sender and less than a certain future value (to allow for network jitter and slight variations in clocks). The window of valid timestamp values that must be guessed by the attacker is governed by the host’s interpretation of TCP timestamp values, which are expected to increase monotonically. Given that these timestamps typically represent the uptime of the host in milliseconds, guessing the exact value can be highly challenging without inside knowledge of the target system's current timestamp counter or the ability to observe legitimate packets in the connection to deduce or narrow down the expected timestamp range. Therefore, while enabling TCP timestamps increases the difficulty of successfully mounting a RST packet attack, it doesn’t make it impossible. However, it adds a significant layer of complexity and uncertainty for the attacker, especially if they are unable to directly observe the traffic between the victim and a legitimate peer to infer the correct timestamp.

answer:The handling of TCP timestamps, including the validation of incoming packets with the Timestamps Option (TSopt), is governed by RFC 7323. According to this RFC, for a TCP segment to be accepted as valid, its timestamp value must not be older than the most recent timestamp received (it must be equal to or greater than the last timestamp received from the sender). However, the RFC does not specify a fixed "future value" threshold for the acceptable range of incoming timestamps, leaving it to implementations to determine how much of a future timestamp deviation they will accept. The tolerance for future timestamp values is implemented to accommodate packets that might appear to be from the "future" due to reasons like clock skew or delays in the network. However, the exact allowable future timestamp range can vary by operating system and its configuration. For practical purposes, you might be looking for how Linux handles this, as it's a common concern. Linux's TCP stack uses a measure called `PAWS_WINDOW` to decide whether to accept or reject packets based on their timestamp. As per the Linux kernel source (as of versions around 4.x onward), this window is defined as 24 days: ```c #define PAWS_WINDOW (60*60*24*24) /* Two months */ ``` This value, which translates to approximately 2,073,600 seconds (or 24 days), provides a broad range to accommodate legitimate packets that might have future timestamps due to the reasons mentioned above. However, it’s crucial to understand that this window is not directly dictating that any future timestamp within 24 days is always acceptable. The primary role of this window is in the context of the PAWS mechanism (Protection Against Wrapped Sequence numbers) to prevent old duplicate segments from disrupting current communications. The actual acceptance of a "future" packet also depends on the relationship between its TCP timestamp and the last received timestamp value, aiming to prevent acceptance of packets that are significantly out of order or are potentially part of an attack. In summary, while there's a technical window for “future” timestamps to be considered valid, this doesn't mean all segments falling within this window are automatically accepted; they must still pass other checks, including sequence number validation and not appearing to be significantly out of order, which could indicate a replay or injection attack rather than legitimate network delay.

answer:No, guessing a sequence number within the receiver's TCP window does not require the attacker to fit their forged RST packet within such a large timestamp window. The attacker must correctly guess a timestamp that closely matches the current expected timestamp range of the target, not necessarily exploit the full PAWS_WINDOW range.

answer:I apologize for any confusion; let me clarify: For a forged RST packet to be accepted by the target, the TCP timestamp value it carries must be more recent than the last valid timestamp received by the target from the legitimate sender but does not necessarily have to explore the full extent of the future window defined by PAWS_WINDOW. The crucial part is that the timestamp must be plausible within the context of recent legitimate traffic between the parties involved. To clarify: - The attacker needs to guess a timestamp that is equal to or greater than the last timestamp received from the legitimate sender. This is to pass the check against the PAWS mechanism, which discards packets with timestamps considered too old. - However, guessing a timestamp that falls within a massive future window (like the 24-day period mentioned) is not specifically the goal or requirement; instead, the guessed timestamp needs to be plausible and relevant to the current state of the connection. It does not mean the attacker aims or needs to leverage the entire 2,073,600 seconds window for their packet to be accepted. In practice, achieving a timestamp within the correct "plausible range" near the last legitimate timestamp is what's necessary for such an attack, which is still quite a challenge without sufficient knowledge of the connection's state.