security: avoid possible config setting override

It may be possible for parsed feed data to override configuration that
is passed to plugins and other components. Normally, feedparser
doesn't send those settings (e.g. output or args) that could
potentially lead to remote code execution exploits. But there *is* one
setting that overlaps right now: "url". It can't do anything now,
because the URL is set *after* the feed is parsed, so it's harmless.

But who knows how feedparser may change in the future? As a security
precaution, we created a list of "locked" items that are important for
us and keep the feed from overriding that.
parent 7f01625e
......@@ -65,6 +65,8 @@ class Feed(feedparser.FeedParserDict):
For all intents and purposes, this can be considered like a dict()
unless otherwise noted.
"""
locked_keys = ('output', 'args', 'filter', 'filter_args',
'folder', 'mailbox', 'url')
def __init__(self, name, *args, **kwargs):
super().__init__(*args, **kwargs)
......@@ -141,8 +143,10 @@ class Feed(feedparser.FeedParserDict):
lock = LOCK
logging.info('parsing feed %s (%d bytes)', self['url'], len(body))
data = feedparser.parse(body)
# add metadata from the feed
self.update(data['feed'])
# add metadata from the feed without overriding user config
for (key, val) in data['feed'].items():
if key not in self and key not in Feed.locked_keys:
self[key] = val
# logging.debug('parsed structure %s',
# json.dumps(data, indent=2, sort_keys=True,
# default=safe_serial))
......@@ -201,6 +205,9 @@ class ConfFeedStorage(configparser.RawConfigParser):
if self.has_section(name):
raise AttributeError('key %s already exists' % name)
d = OrderedDict()
# when a new element is added here, it must be added to the
# Feed.locked_keys config to keep parsed feed elements from
# overriding potentially secure-sensitive settings
d['url'] = url
if output is not None:
d['output'] = output
......
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