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14c2920 Imported Upstream version 1.5.18
Antonio Radici authored
1 $Id$
2
3 Recently, there have been reports on security problems induced by
4 the interpretation of shell meta-characters embedded in MIME
5 parameters. These reports were referring to Pine, but the problem
6 also applied when using mutt.
7
8 More precisely, a mailcap entry like this one would lead to
9 problems:
10
11 > text/test-mailcap-bug; cat %s; copiousoutput; \
12 > test=test "`echo %{charset} | tr '[A-Z]' '[a-z]'`" != iso-8859-1
13
14 When expanded with a charset parameter of ``touch${IFS}ME``, a file
15 named "ME" would be created in the current directory.
16
17 While we don't completely agree that this is an actual MUA problem
18 (see below), we have implemented a couple of fixes for this:
19
20 - Backticks are handled specially when preparing % expandos for
21 mailcap entries. This fix will keep the current problem from
22 occuring, but we are sure there are other possible mailcap entries
23 where this doesn't help.
24
25 - We have added a configuration variable named $mailcap_sanitize,
26 which is set by default. If set, mutt will restrict possible
27 characters in mailcap % expandos to a well-defined set of safe
28 characters. This is the safe setting, but we are not sure it
29 doesn't break some more advanced MIME stuff.
30
31 >>> DON'T UNSET THIS OPTION UNLESS YOU KNOW WHAT YOU ARE DOING.
32
33
34 Anyway, this problem is not necessarily a problem which should be
35 solved inside the MUA, as it's difficult (maybe impossible) to solve
36 there. Additionally, there is more than one program which parses
37 mailcap. So writing secure mailcap statements is generally a good
38 idea. We encourage you to do this.
39
40 The most basic rule is this one:
41
42 >>> KEEP THE %-EXPANDOS AWAY FROM SHELL QUOTING.
43
44 Don't quote them with single or double quotes. Mutt does this for
45 you, the right way, as should any other program which interprets
46 mailcap. Don't put them into backtick expansions - as you have seen
47 above, this is a recipe for disaster. Be highly careful with eval
48 statements, and avoid them if possible at all.
49
50 If you have to use the %-expandos' values in context where you need
51 quoting or backtick expansions, put that value into a shell variable
52 and reference the shell variable where necessary (possibly with the
53 proper quoting put around it, like in "$charset").
54
55 For example, a safe version of the mailcap statement above could
56 look like this:
57
58 > text/test-mailcap-bug; cat %s; copiousoutput; test=charset=%{charset} \
59 > && test "`echo \"$charset\" | tr '[A-Z]' '[a-z]'`" != iso-8859-1
60
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