diff --git a/changelog.d/5133.bugfix b/changelog.d/5133.bugfix
new file mode 100644
index 0000000000..be6474a692
--- /dev/null
+++ b/changelog.d/5133.bugfix
@@ -0,0 +1 @@
+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!
diff --git a/changelog.d/5134.bugfix b/changelog.d/5134.bugfix
new file mode 100644
index 0000000000..684d48c53a
--- /dev/null
+++ b/changelog.d/5134.bugfix
@@ -0,0 +1 @@
+Blacklist 0.0.0.0 and :: by default for URL previews. Thanks to @opnsec for identifying and responsibly disclosing this issue too!
diff --git a/docs/sample_config.yaml b/docs/sample_config.yaml
index fa2bccd5ef..84337a7c72 100644
--- a/docs/sample_config.yaml
+++ b/docs/sample_config.yaml
@@ -548,11 +548,12 @@ 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
@@ -562,6 +563,12 @@ 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'
@@ -572,7 +579,7 @@ 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
diff --git a/synapse/config/repository.py b/synapse/config/repository.py
index 3f34ad9b2a..fbfcecc240 100644
--- a/synapse/config/repository.py
+++ b/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?
+ #
+ # 'false' by default: uncomment the following to enable it (and specify a
+ # url_preview_ip_range_blacklist blacklist).
#
- #url_preview_enabled: false
+ #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
diff --git a/synapse/util/stringutils.py b/synapse/util/stringutils.py
index fdcb375f95..69dffd8244 100644
--- a/synapse/util/stringutils.py
+++ b/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)
)
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