--- a/sys/kern/kern_sysctl.c
+++ b/sys/kern/kern_sysctl.c
@@ -47,6 +47,7 @@
 #include <sys/malloc.h>
 #include <sys/proc.h>
 #include <sys/caps.h>
+#include <sys/jail.h>
 #include <sys/sysmsg.h>
 #include <sys/lock.h>
 #include <sys/sbuf.h>
@@ -1449,6 +1450,20 @@
 		return (error);
 	}
 
+	/*
+	 * A confined (jailed) root may only write nodes explicitly
+	 * marked CTLFLAG_PRISON ("prisoned roots can fiddle").
+	 * prison_priv_check() deliberately allows SYSCAP_NOSYSCTL_WR
+	 * inside jails, so without this check a jailed uid-0 can mutate
+	 * host-global state (kern.maxfiles, kern.securelevel, debug.*,
+	 * net.*, ...) even though CTLFLAG_PRISON exists for exactly
+	 * this purpose and is honored nowhere.
+	 */
+	if (req->newptr && td->td_ucred && jailed(td->td_ucred) &&
+	    (oid->oid_kind & CTLFLAG_PRISON) == 0) {
+		return (EPERM);
+	}
+
 	if (oid->oid_handler == NULL)
 		return EINVAL;
 
--- a/sys/kern/kern_proc.c
+++ b/sys/kern/kern_proc.c
@@ -2202,7 +2202,7 @@
 
 
 SYSCTL_NODE(_kern_proc, KERN_PROC_ARGS, args,
-	CTLFLAG_RW | CTLFLAG_ANYBODY | CTLFLAG_NOLOCK,
+	CTLFLAG_RW | CTLFLAG_ANYBODY | CTLFLAG_PRISON | CTLFLAG_NOLOCK,
 	sysctl_kern_proc_args, "Process argument list");
 
 SYSCTL_NODE(_kern_proc, KERN_PROC_CWD, cwd,