plugins run in taint mode because the uid is changed, so the path must not
contain writable directories.

--- node/sbin/munin-run.orig	2020-03-09 01:59:44 UTC
+++ node/sbin/munin-run
@@ -118,6 +118,9 @@ sub main
         $ENV{$key} =~ /^(.*)$/s;
         $ENV{$key} = $1;
     }
+    # plugins run in taint mode because the uid is changed, so the path
+    # must not contain writable directories.
+    $ENV{PATH}='/bin:/sbin:/usr/bin:/usr/sbin:%%PREFIX%%/bin:%%PREFIX%%/sbin';
 
     $0 =~ /^(.*)$/;
     $0 = $1;