バージョン確認
dpkg -l bash

apt-get update
apt-get upgrade
で更新。

詳細確認は、
zcat /usr/share/doc/bash/changelog.Debian.gz |head -20
などとすると
bash (4.2-2ubuntu2.5) precise-security; urgency=medium

* SECURITY UPDATE: out-of-bounds memory access
- debian/patches/CVE-2014-718x.diff: guard against overflow and fix
off-by-one in bash/parse.y.
- CVE-2014-7186
- CVE-2014-7187
* SECURITY IMPROVEMENT: use prefixes and suffixes for function exports
- debian/patches/variables-affix.diff: add prefixes and suffixes in
bash/variables.c.

-- Marc Deslauriers Fri, 26 Sep 2014 13:27:53 -0400

bash (4.2-2ubuntu2.3) precise-security; urgency=medium

* SECURITY UPDATE: incomplete fix for CVE-2014-6271
- debian/patches/CVE-2014-7169.diff: fix logic in bash/parse.y.
- CVE-2014-7169

-- Marc Deslauriers Thu, 25 Sep 2014 02:11:10 -0400
のように確認できる。