changelog tweaks

Blacklist 0.0.0.0 and :: by default for URL previews

CHANGES.md

@@ -1,3 +1,14 @@
+Synapse 0.99.3.1 (2019-05-03)
+=============================
+
+Security update
+---------------
+
+This release includes two security fixes:
+
+- Switch to using a cryptographically-secure random number generator for token strings, ensuring they cannot be predicted by an attacker. Thanks to @opnsec for identifying and responsibly disclosing this issue! ([\#5133](https://github.com/matrix-org/synapse/issues/5133))
+- Blacklist 0.0.0.0 and :: by default for URL previews. Thanks to @opnsec for identifying and responsibly disclosing this issue too! ([\#5134](https://github.com/matrix-org/synapse/issues/5134))
+
 Synapse 0.99.3 (2019-04-01)
 ===========================
 

debian/changelog

@@ -1,3 +1,9 @@
+matrix-synapse-py3 (0.99.3.1) stable; urgency=medium
+
+  * New synapse release 0.99.3.1.
+
+ -- Synapse Packaging team <packages@matrix.org>  Fri, 03 May 2019 16:02:43 +0100
+
 matrix-synapse-py3 (0.99.3) stable; urgency=medium
 
   [ Richard van der Hoff ]

docs/sample_config.yaml

@@ -506,11 +506,12 @@ uploads_path: "DATADIR/uploads"
 #    height: 600
 #    method: scale
 
-# Is the preview URL API enabled?  If enabled, you *must* specify
-# an explicit url_preview_ip_range_blacklist of IPs that the spider is
-# denied from accessing.
+# Is the preview URL API enabled?
 #
-#url_preview_enabled: false
+# 'false' by default: uncomment the following to enable it (and specify a
+# url_preview_ip_range_blacklist blacklist).
+#
+#url_preview_enabled: true
 
 # List of IP address CIDR ranges that the URL preview spider is denied
 # from accessing.  There are no defaults: you must explicitly
@@ -520,6 +521,12 @@ uploads_path: "DATADIR/uploads"
 # synapse to issue arbitrary GET requests to your internal services,
 # causing serious security issues.
 #
+# (0.0.0.0 and :: are always blacklisted, whether or not they are explicitly
+# listed here, since they correspond to unroutable addresses.)
+#
+# This must be specified if url_preview_enabled is set. It is recommended that 
+# you uncomment the following list as a starting point.
+#
 #url_preview_ip_range_blacklist:
 #  - '127.0.0.0/8'
 #  - '10.0.0.0/8'
@@ -530,7 +537,7 @@ uploads_path: "DATADIR/uploads"
 #  - '::1/128'
 #  - 'fe80::/64'
 #  - 'fc00::/7'
-#
+
 # List of IP address CIDR ranges that the URL preview spider is allowed
 # to access even if they are specified in url_preview_ip_range_blacklist.
 # This is useful for specifying exceptions to wide-ranging blacklisted

synapse/__init__.py

@@ -27,4 +27,4 @@ try:
 except ImportError:
     pass
 
-__version__ = "0.99.3"
+__version__ = "0.99.3.1"

synapse/config/repository.py

@@ -186,17 +186,21 @@ class ContentRepositoryConfig(Config):
             except ImportError:
                 raise ConfigError(MISSING_NETADDR)
 
-            if "url_preview_ip_range_blacklist" in config:
-                self.url_preview_ip_range_blacklist = IPSet(
-                    config["url_preview_ip_range_blacklist"]
-                )
-            else:
+            if "url_preview_ip_range_blacklist" not in config:
                 raise ConfigError(
                     "For security, you must specify an explicit target IP address "
                     "blacklist in url_preview_ip_range_blacklist for url previewing "
                     "to work"
                 )
 
+            self.url_preview_ip_range_blacklist = IPSet(
+                config["url_preview_ip_range_blacklist"]
+            )
+
+            # we always blacklist '0.0.0.0' and '::', which are supposed to be
+            # unroutable addresses.
+            self.url_preview_ip_range_blacklist.update(['0.0.0.0', '::'])
+
             self.url_preview_ip_range_whitelist = IPSet(
                 config.get("url_preview_ip_range_whitelist", ())
             )
@@ -260,11 +264,12 @@ class ContentRepositoryConfig(Config):
         #thumbnail_sizes:
 %(formatted_thumbnail_sizes)s
 
-        # Is the preview URL API enabled?  If enabled, you *must* specify
-        # an explicit url_preview_ip_range_blacklist of IPs that the spider is
-        # denied from accessing.
+        # Is the preview URL API enabled?
         #
-        #url_preview_enabled: false
+        # 'false' by default: uncomment the following to enable it (and specify a
+        # url_preview_ip_range_blacklist blacklist).
+        #
+        #url_preview_enabled: true
 
         # List of IP address CIDR ranges that the URL preview spider is denied
         # from accessing.  There are no defaults: you must explicitly
@@ -274,6 +279,12 @@ class ContentRepositoryConfig(Config):
         # synapse to issue arbitrary GET requests to your internal services,
         # causing serious security issues.
         #
+        # (0.0.0.0 and :: are always blacklisted, whether or not they are explicitly
+        # listed here, since they correspond to unroutable addresses.)
+        #
+        # This must be specified if url_preview_enabled is set. It is recommended that
+        # you uncomment the following list as a starting point.
+        #
         #url_preview_ip_range_blacklist:
         #  - '127.0.0.0/8'
         #  - '10.0.0.0/8'
@@ -284,7 +295,7 @@ class ContentRepositoryConfig(Config):
         #  - '::1/128'
         #  - 'fe80::/64'
         #  - 'fc00::/7'
-        #
+
         # List of IP address CIDR ranges that the URL preview spider is allowed
         # to access even if they are specified in url_preview_ip_range_blacklist.
         # This is useful for specifying exceptions to wide-ranging blacklisted

synapse/util/stringutils.py

@@ -24,14 +24,19 @@ _string_with_symbols = (
     string.digits + string.ascii_letters + ".,;:^&*-_+=#~@"
 )
 
+# random_string and random_string_with_symbols are used for a range of things,
+# some cryptographically important, some less so. We use SystemRandom to make sure
+# we get cryptographically-secure randoms.
+rand = random.SystemRandom()
+
 
 def random_string(length):
-    return ''.join(random.choice(string.ascii_letters) for _ in range(length))
+    return ''.join(rand.choice(string.ascii_letters) for _ in range(length))
 
 
 def random_string_with_symbols(length):
     return ''.join(
-        random.choice(_string_with_symbols) for _ in range(length)
+        rand.choice(_string_with_symbols) for _ in range(length)
     )