gnupg -- false positive signature verification

Werner Koch reports:

The Gentoo project identified a security related bug in
GnuPG. When using any current version of GnuPG for
unattended signature verification (e.g. by scripts and
mail programs), false positive signature verification of
detached signatures may occur.
This problem affects the tool gpgv, as well as using
“gpg --verify” to imitate gpgv, if only the exit code of
the process is used to decide whether a detached signature
is valid. This is a plausible mode of operation for
gpgv.
If, as suggested, the --status-fd generated output is
used to decide whether a signature is valid, no problem
exists. In particular applications making use of the
GPGME library[2] are not affected.