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gh-68966: Make mailcap refuse to match unsafe filenames/types/params (GH-91993)
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@ -60,6 +60,18 @@ standard. However, mailcap files are supported on most Unix systems.
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use) to determine whether or not the mailcap line applies. :func:`findmatch`
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will automatically check such conditions and skip the entry if the check fails.
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.. versionchanged:: 3.11
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To prevent security issues with shell metacharacters (symbols that have
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special effects in a shell command line), ``findmatch`` will refuse
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to inject ASCII characters other than alphanumerics and ``@+=:,./-_``
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into the returned command line.
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If a disallowed character appears in *filename*, ``findmatch`` will always
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return ``(None, None)`` as if no entry was found.
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If such a character appears elsewhere (a value in *plist* or in *MIMEtype*),
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``findmatch`` will ignore all mailcap entries which use that value.
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A :mod:`warning <warnings>` will be raised in either case.
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.. function:: getcaps()
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@ -2,6 +2,7 @@
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import os
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import warnings
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import re
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__all__ = ["getcaps","findmatch"]
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@ -19,6 +20,11 @@ def lineno_sort_key(entry):
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else:
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return 1, 0
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_find_unsafe = re.compile(r'[^\xa1-\U0010FFFF\w@+=:,./-]').search
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class UnsafeMailcapInput(Warning):
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"""Warning raised when refusing unsafe input"""
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# Part 1: top-level interface.
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@ -171,15 +177,22 @@ def findmatch(caps, MIMEtype, key='view', filename="/dev/null", plist=[]):
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entry to use.
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"""
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if _find_unsafe(filename):
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msg = "Refusing to use mailcap with filename %r. Use a safe temporary filename." % (filename,)
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warnings.warn(msg, UnsafeMailcapInput)
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return None, None
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entries = lookup(caps, MIMEtype, key)
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# XXX This code should somehow check for the needsterminal flag.
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for e in entries:
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if 'test' in e:
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test = subst(e['test'], filename, plist)
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if test is None:
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continue
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if test and os.system(test) != 0:
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continue
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command = subst(e[key], MIMEtype, filename, plist)
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return command, e
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if command is not None:
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return command, e
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return None, None
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def lookup(caps, MIMEtype, key=None):
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@ -212,6 +225,10 @@ def subst(field, MIMEtype, filename, plist=[]):
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elif c == 's':
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res = res + filename
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elif c == 't':
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if _find_unsafe(MIMEtype):
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msg = "Refusing to substitute MIME type %r into a shell command." % (MIMEtype,)
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warnings.warn(msg, UnsafeMailcapInput)
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return None
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res = res + MIMEtype
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elif c == '{':
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start = i
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@ -219,7 +236,12 @@ def subst(field, MIMEtype, filename, plist=[]):
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i = i+1
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name = field[start:i]
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i = i+1
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res = res + findparam(name, plist)
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param = findparam(name, plist)
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if _find_unsafe(param):
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msg = "Refusing to substitute parameter %r (%s) into a shell command" % (param, name)
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warnings.warn(msg, UnsafeMailcapInput)
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return None
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res = res + param
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# XXX To do:
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# %n == number of parts if type is multipart/*
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# %F == list of alternating type and filename for parts
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@ -128,7 +128,8 @@ def test_subst(self):
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(["", "audio/*", "foo.txt"], ""),
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(["echo foo", "audio/*", "foo.txt"], "echo foo"),
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(["echo %s", "audio/*", "foo.txt"], "echo foo.txt"),
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(["echo %t", "audio/*", "foo.txt"], "echo audio/*"),
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(["echo %t", "audio/*", "foo.txt"], None),
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(["echo %t", "audio/wav", "foo.txt"], "echo audio/wav"),
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(["echo \\%t", "audio/*", "foo.txt"], "echo %t"),
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(["echo foo", "audio/*", "foo.txt", plist], "echo foo"),
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(["echo %{total}", "audio/*", "foo.txt", plist], "echo 3")
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@ -212,7 +213,10 @@ def test_findmatch(self):
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('"An audio fragment"', audio_basic_entry)),
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([c, "audio/*"],
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{"filename": fname},
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("/usr/local/bin/showaudio audio/*", audio_entry)),
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(None, None)),
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([c, "audio/wav"],
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{"filename": fname},
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("/usr/local/bin/showaudio audio/wav", audio_entry)),
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([c, "message/external-body"],
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{"plist": plist},
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("showexternal /dev/null default john python.org /tmp foo bar", message_entry))
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@ -0,0 +1,4 @@
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The deprecated mailcap module now refuses to inject unsafe text (filenames,
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MIME types, parameters) into shell commands. Instead of using such text, it
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will warn and act as if a match was not found (or for test commands, as if
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the test failed).
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