Remote activity disclosure via acknowledgment timing

Timing side channel in IETF TCP RFC 9293 allows remote attackers to infer a client's concurrent web or video activity through RTT measurements. An attacker-controlled server sends a slow HTTP response and measures TCP acknowledgment round-trip times, which rise when the victim's last-mile bottleneck buffers concurrent traffic. Exploitation requires the victim to maintain that slow connection while other traffic crosses the same bottleneck; the demonstrated consequence is inference of visited websites or watched videos.