@@ -60,6 +60,18 @@ standard. However, mailcap files are supported on most Unix systems.

use) to determine whether or not the mailcap line applies. :func:`findmatch`

will automatically check such conditions and skip the entry if the check fails.

.. versionchanged:: 3.10.8

To prevent security issues with shell metacharacters (symbols that have

special effects in a shell command line), ``findmatch`` will refuse

to inject ASCII characters other than alphanumerics and ``@+=:,./-_``

into the returned command line.

If a disallowed character appears in *filename*, ``findmatch`` will always

return ``(None, None)`` as if no entry was found.

If such a character appears elsewhere (a value in *plist* or in *MIMEtype*),

``findmatch`` will ignore all mailcap entries which use that value.

A :mod:`warning <warnings>` will be raised in either case.

.. function:: getcaps()

@@ -2338,3 +2338,11 @@ line flag, or :mod:`sys` APIs. See the :ref:`integer string conversion

length limitation <int_max_str_digits>` documentation. The default limit

is 4300 digits in string form.

Notable security feature in 3.10.8

==================================

The deprecated :mod:`mailcap` module now refuses to inject unsafe text

(filenames, MIME types, parameters) into shell commands. Instead of using such

text, it will warn and act as if a match was not found (or for test commands,

as if the test failed).

(Contributed by Petr Viktorin in :gh:`98966`.)

@@ -2,6 +2,7 @@

import os

import warnings

import re

__all__ = ["getcaps","findmatch"]

@@ -13,6 +14,11 @@ def lineno_sort_key(entry):

else:

return 1, 0

_find_unsafe = re.compile(r'[^\xa1-\U0010FFFF\w@+=:,./-]').search

class UnsafeMailcapInput(Warning):

"""Warning raised when refusing unsafe input"""

# Part 1: top-level interface.

@@ -165,15 +171,22 @@ def findmatch(caps, MIMEtype, key='view', filename="/dev/null", plist=[]):

entry to use.

"""

if _find_unsafe(filename):

msg = "Refusing to use mailcap with filename %r. Use a safe temporary filename." % (filename,)

warnings.warn(msg, UnsafeMailcapInput)

return None, None

entries = lookup(caps, MIMEtype, key)

# XXX This code should somehow check for the needsterminal flag.

for e in entries:

if 'test' in e:

test = subst(e['test'], filename, plist)

if test is None:

continue

if test and os.system(test) != 0:

continue

command = subst(e[key], MIMEtype, filename, plist)

return command, e

if command is not None:

return command, e

return None, None

def lookup(caps, MIMEtype, key=None):

@@ -206,14 +219,23 @@ def subst(field, MIMEtype, filename, plist=[]):

elif c == 's':

res = res + filename

elif c == 't':

if _find_unsafe(MIMEtype):

msg = "Refusing to substitute MIME type %r into a shell command." % (MIMEtype,)

warnings.warn(msg, UnsafeMailcapInput)

return None

res = res + MIMEtype

elif c == '{':

start = i

while i < n and field[i] != '}':

i = i+1

name = field[start:i]

i = i+1

res = res + findparam(name, plist)

param = findparam(name, plist)

if _find_unsafe(param):

msg = "Refusing to substitute parameter %r (%s) into a shell command" % (param, name)

warnings.warn(msg, UnsafeMailcapInput)

return None

res = res + param

# XXX To do:

# %n == number of parts if type is multipart/*

# %F == list of alternating type and filename for parts

@@ -123,7 +123,8 @@ def test_subst(self):

(["", "audio/*", "foo.txt"], ""),

(["echo foo", "audio/*", "foo.txt"], "echo foo"),

(["echo %s", "audio/*", "foo.txt"], "echo foo.txt"),

(["echo %t", "audio/*", "foo.txt"], "echo audio/*"),

(["echo %t", "audio/*", "foo.txt"], None),

(["echo %t", "audio/wav", "foo.txt"], "echo audio/wav"),

(["echo \\%t", "audio/*", "foo.txt"], "echo %t"),

(["echo foo", "audio/*", "foo.txt", plist], "echo foo"),

(["echo %{total}", "audio/*", "foo.txt", plist], "echo 3")

@@ -207,7 +208,10 @@ def test_findmatch(self):

('"An audio fragment"', audio_basic_entry)),

([c, "audio/*"],

{"filename": fname},

("/usr/local/bin/showaudio audio/*", audio_entry)),

(None, None)),

([c, "audio/wav"],

{"filename": fname},

("/usr/local/bin/showaudio audio/wav", audio_entry)),

([c, "message/external-body"],

{"plist": plist},

("showexternal /dev/null default john python.org /tmp foo bar", message_entry))

@@ -0,0 +1,4 @@

The deprecated mailcap module now refuses to inject unsafe text (filenames,

MIME types, parameters) into shell commands. Instead of using such text, it

will warn and act as if a match was not found (or for test commands, as if

the test failed).