■ GnuPG 1.4.2.1

Web上で変更点が見つからなかったのでダウンロードしてNEWSを見たところ以下のような記述がありました。

Noteworthy changes in version 1.4.2.1 (2006-02-14)
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    * Security fix for a verification weakness in gpgv.  Some input
      could lead to gpgv exiting with 0 even if the detached signature
      file did not carry any signature.  This is not as fatal as it
      might seem because the suggestion as always been not to rely on
      th exit code but to parse the --status-fd messages.  However it
      is likely that gpgv is used in that simplified way and thus we
      do this release.  Same problem with "gpg --verify" but nobody
      should have used this for signature verification without
      checking the status codes anyway.  Thanks to the taviso from
      Gentoo for reporting this problem.

QMAIL3でGnuPGを使って署名の検証をする場合には、--status-fdを使っているので大丈夫だと思われます。