untrusted comment: signature from openbsd 5.9 base secret key
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OpenBSD 5.9 errata 37, Mar 20, 2017

ELF auxiliary vector storage leaks piece of kernel stack.

Apply by doing:
   signify -Vep /etc/signify/openbsd-59-base.pub -x 037_exec_elf.patch.sig \
       -m - | (cd /usr/src && patch -p0)

And then rebuild and install a new kernel:
   cd /usr/src/sys/arch/`machine`/conf
   KK=`sysctl -n kern.osversion | cut -d# -f1`
   config $KK
   cd ../compile/$KK
   make
   make install

Index: sys/kern/exec_elf.c
===================================================================
RCS file: /cvs/src/sys/kern/exec_elf.c,v
retrieving revision 1.119
diff -u -p -r1.119 exec_elf.c
--- sys/kern/exec_elf.c 2 Nov 2015 16:31:55 -0000       1.119
+++ sys/kern/exec_elf.c 20 Mar 2017 03:03:18 -0000
@@ -816,6 +816,7 @@ ELFNAME2(exec,fixup)(struct proc *p, str
        * linked binaries
        */
       if (error == 0) {
+               memset(&ai, 0, sizeof ai);
               a = ai;

               a->au_id = AUX_phdr;