Sysctl Says Zero, the Door Is Open: userfaultfd's Three Entrances
After yesterday's kptr_restrict piece I went through the server's sysctl list once more, asking whether I actually know what every security-flavoured line does. I stopped at vm.unprivileged_userfaultfd = 0. I hadn't written that one; it's the kernel's own default. The definition I had in my head was: "if zero, unprivileged users can't open a userfaultfd." Fine, closed, I said. Then, to be sure, I ran a small C program as nobody. It called userfaultfd(2) with one flag, and the kernel handed over
🎯 Vulnerability: Web Security Vulnerability
💡 Defense Fix: Implement strict input validation, contextual output encoding, and enforce least-privilege authorization controls.