diff options
| -rw-r--r-- | Doc/library/mailcap.rst | 12 | ||||
| -rw-r--r-- | Lib/mailcap.py | 26 | ||||
| -rw-r--r-- | Lib/test/test_mailcap.py | 8 | ||||
| -rw-r--r-- | Misc/NEWS.d/next/Security/2022-04-27-18-25-30.gh-issue-68966.gjS8zs.rst | 4 |
4 files changed, 46 insertions, 4 deletions
diff --git a/Doc/library/mailcap.rst b/Doc/library/mailcap.rst index 5490c84..bfaedb4 100644 --- a/Doc/library/mailcap.rst +++ b/Doc/library/mailcap.rst @@ -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:: 3.11 + + 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() diff --git a/Lib/mailcap.py b/Lib/mailcap.py index 856b6a5..7278ea7 100644 --- a/Lib/mailcap.py +++ b/Lib/mailcap.py @@ -2,6 +2,7 @@ import os import warnings +import re __all__ = ["getcaps","findmatch"] @@ -19,6 +20,11 @@ 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. @@ -171,15 +177,22 @@ 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): @@ -212,6 +225,10 @@ 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 @@ -219,7 +236,12 @@ def subst(field, MIMEtype, filename, plist=[]): 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 diff --git a/Lib/test/test_mailcap.py b/Lib/test/test_mailcap.py index d3995b1..8185f4a 100644 --- a/Lib/test/test_mailcap.py +++ b/Lib/test/test_mailcap.py @@ -128,7 +128,8 @@ class HelperFunctionTest(unittest.TestCase): (["", "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") @@ -212,7 +213,10 @@ class FindmatchTest(unittest.TestCase): ('"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)) diff --git a/Misc/NEWS.d/next/Security/2022-04-27-18-25-30.gh-issue-68966.gjS8zs.rst b/Misc/NEWS.d/next/Security/2022-04-27-18-25-30.gh-issue-68966.gjS8zs.rst new file mode 100644 index 0000000..da81a1f --- /dev/null +++ b/Misc/NEWS.d/next/Security/2022-04-27-18-25-30.gh-issue-68966.gjS8zs.rst @@ -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). |