[Python-checkins] [3.7] gh-68966: Make mailcap refuse to match unsafe filenames/types/params (GH-91993) (GH-98191)
ambv
webhook-mailer at python.org
Tue Oct 11 16:27:19 EDT 2022
https://github.com/python/cpython/commit/6e8e9e7c030b6236ff220362944cba1b93c84bc4
commit: 6e8e9e7c030b6236ff220362944cba1b93c84bc4
branch: 3.7
author: Miss Islington (bot) <31488909+miss-islington at users.noreply.github.com>
committer: ambv <lukasz at langa.pl>
date: 2022-10-11T22:27:14+02:00
summary:
[3.7] gh-68966: Make mailcap refuse to match unsafe filenames/types/params (GH-91993) (GH-98191)
gh-68966: Make mailcap refuse to match unsafe filenames/types/params (GH-91993)
(cherry picked from commit b9509ba7a9c668b984dab876c7926fe1dc5aa0ba)
Co-authored-by: Petr Viktorin <encukou at gmail.com>
files:
A Misc/NEWS.d/next/Security/2022-04-27-18-25-30.gh-issue-68966.gjS8zs.rst
M Doc/library/mailcap.rst
M Lib/mailcap.py
M Lib/test/test_mailcap.py
diff --git a/Doc/library/mailcap.rst b/Doc/library/mailcap.rst
index bf9639bdaca5..a75857be623e 100644
--- a/Doc/library/mailcap.rst
+++ b/Doc/library/mailcap.rst
@@ -54,6 +54,18 @@ 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 bd0fc0981c8c..dcd4b449e828 100644
--- a/Lib/mailcap.py
+++ b/Lib/mailcap.py
@@ -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 at +=:,./-]').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):
@@ -206,6 +219,10 @@ 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
@@ -213,7 +230,12 @@ 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 c08423c67073..920283d9a2e3 100644
--- a/Lib/test/test_mailcap.py
+++ b/Lib/test/test_mailcap.py
@@ -121,7 +121,8 @@ 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")
@@ -205,7 +206,10 @@ 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))
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 000000000000..da81a1f6993d
--- /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).
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