diff --git a/UPDATING b/UPDATING
index 7aa936bf4550..130a3b3a5120 100644
--- a/UPDATING
+++ b/UPDATING
@@ -31,6 +31,12 @@ NOTE TO PEOPLE WHO THINK THAT FreeBSD 10.x IS SLOW:
 	disable the most expensive debugging functionality run
 	"ln -s 'abort:false,junk:false' /etc/malloc.conf".)
 
+20130618:
+	Fix a bug that allowed a tracing process (e.g. gdb) to write
+	to a memory-mapped file in the traced process's address space
+	even if neither the traced process nor the tracing process had
+	write access to that file.
+
 20130615:
 	CVS has been removed from the base system.  An exact copy
 	of the code is available from the devel/cvs port.
diff --git a/sys/vm/vm_map.c b/sys/vm/vm_map.c
index a9ae8030dde9..1fee839b9895 100644
--- a/sys/vm/vm_map.c
+++ b/sys/vm/vm_map.c
@@ -3807,6 +3807,12 @@ RetryLookup:;
 		vm_map_unlock_read(map);
 		return (KERN_PROTECTION_FAILURE);
 	}
+	if ((fault_typea & VM_PROT_COPY) != 0 &&
+	    (entry->max_protection & VM_PROT_WRITE) == 0 &&
+	    (entry->eflags & MAP_ENTRY_COW) == 0) {
+		vm_map_unlock_read(map);
+		return (KERN_PROTECTION_FAILURE);
+	}
 
 	/*
 	 * If this page is not pageable, we have to get it for all possible