Matej Cepl
83bcadedd7
CVE-2015-20107 (bsc#1198511, gh#python/cpython#68966), the command injection in the mailcap module. OBS-URL: https://build.opensuse.org/package/show/devel:languages:python:Factory/python310?expand=0&rev=40
137 lines
5.6 KiB
Diff
137 lines
5.6 KiB
Diff
From c3e7f139b440d7424986204e9f3fc2275aea3377 Mon Sep 17 00:00:00 2001
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From: Petr Viktorin <encukou@gmail.com>
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Date: Wed, 27 Apr 2022 18:17:33 +0200
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Subject: [PATCH 1/4] gh-68966: Make mailcap refuse to match unsafe
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filenames/types/params
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---
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Doc/library/mailcap.rst | 12 ++++
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Lib/mailcap.py | 26 +++++++++-
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Lib/test/test_mailcap.py | 8 ++-
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Misc/NEWS.d/next/Security/2022-04-27-18-25-30.gh-issue-68966.gjS8zs.rst | 4 +
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4 files changed, 46 insertions(+), 4 deletions(-)
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--- a/Doc/library/mailcap.rst
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+++ b/Doc/library/mailcap.rst
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@@ -60,6 +60,18 @@ standard. However, mailcap files are su
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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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+
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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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+
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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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--- a/Lib/mailcap.py
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+++ b/Lib/mailcap.py
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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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@@ -13,6 +14,11 @@ 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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+
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+class UnsafeMailcapInput(Warning):
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+ """Warning raised when refusing unsafe input"""
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+
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# Part 1: top-level interface.
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@@ -165,15 +171,22 @@ def findmatch(caps, MIMEtype, key='view'
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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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@@ -206,6 +219,10 @@ def subst(field, MIMEtype, filename, pli
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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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@@ -213,7 +230,12 @@ def subst(field, MIMEtype, filename, pli
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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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--- a/Lib/test/test_mailcap.py
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+++ b/Lib/test/test_mailcap.py
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@@ -123,7 +123,8 @@ class HelperFunctionTest(unittest.TestCa
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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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@@ -207,7 +208,10 @@ class FindmatchTest(unittest.TestCase):
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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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--- /dev/null
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+++ b/Misc/NEWS.d/next/Security/2022-04-27-18-25-30.gh-issue-68966.gjS8zs.rst
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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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