#tcp

This week I'm looking at TCP flags. What exactly are they signaling? What responses can you expect? https://ubritsa.com/posts/tcp-raising-the-wrong-flags/ #TCP #Flags #Scanning #Nmap #Reconnaissance #RFC793 #Layer4 #StatefulInspection

Here are some things that one can add to the analysis of the MacOS TCP timeout clock freeze bug. The code for calculate_tcp_clock() in XNU was changed in May 2025. Older versions of this function (e.g. in xnu-11417) worked quite differently and wouldn't have stopped ticking the clock at 32-bit unsigned integer wraparound. None of #NetBSD, #FreeBSD, nor #OpenBSD share this exact way of doing TCP timeout processing with #XNU. FreeBSD does not have a tcp_now and works off the global 32-bit ticks variable. OpenBSD effectively works off the kernel's system clock, too, but with a randomized offset, and does 64-bit unsigned modular arithmetic. NetBSD uses a distinct 32-bit unsigned tcp_now counter that it simply increments by 1 at regular intervals, and does modular arithmetic subtraction. https://photon.codes/blog/we-found-a-ticking-time-bomb-in-macos-tcp-networking #TCP #MacOS