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authorRichard van der Hoff <richard@matrix.org>2019-05-03 12:38:03 +0100
committerRichard van der Hoff <richard@matrix.org>2019-05-03 13:02:55 +0100
commit247dc1bd0bd9ee2b9525495c0dbd819baf10ec1f (patch)
tree05f2ee2721066eea82e9605b9f5ce32f379e6fda
parent0.99.2 (diff)
downloadsynapse-247dc1bd0bd9ee2b9525495c0dbd819baf10ec1f.tar.xz
Use SystemRandom for token generation
-rw-r--r--changelog.d/5133.bugfix1
-rw-r--r--synapse/util/stringutils.py9
2 files changed, 8 insertions, 2 deletions
diff --git a/changelog.d/5133.bugfix b/changelog.d/5133.bugfix
new file mode 100644
index 0000000000..12a32a906b
--- /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 for identifying and responsibly disclosing this issue!
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)
     )