Merge pull request #8142 from FiloSottile/filippo/updates

[update] fix (unexploitable) BB'06 vulnerability in rsa_verify

test/test_update.py

@@ -0,0 +1,30 @@
+#!/usr/bin/env python
+
+from __future__ import unicode_literals
+
+# Allow direct execution
+import os
+import sys
+import unittest
+sys.path.insert(0, os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
+
+
+import json
+from youtube_dl.update import rsa_verify
+
+
+class TestUpdate(unittest.TestCase):
+    def test_rsa_verify(self):
+        UPDATES_RSA_KEY = (0x9d60ee4d8f805312fdb15a62f87b95bd66177b91df176765d13514a0f1754bcd2057295c5b6f1d35daa6742c3ffc9a82d3e118861c207995a8031e151d863c9927e304576bc80692bc8e094896fcf11b66f3e29e04e3a71e9a11558558acea1840aec37fc396fb6b65dc81a1c4144e03bd1c011de62e3f1357b327d08426fe93, 65537)
+        with open(os.path.join(os.path.dirname(os.path.abspath(__file__)), 'versions.json'), 'rb') as f:
+            versions_info = f.read().decode()
+        versions_info = json.loads(versions_info)
+        signature = versions_info['signature']
+        del versions_info['signature']
+        self.assertTrue(rsa_verify(
+            json.dumps(versions_info, sort_keys=True).encode('utf-8'),
+            signature, UPDATES_RSA_KEY))
+
+
+if __name__ == '__main__':
+    unittest.main()

test/versions.json

@@ -0,0 +1,34 @@
+{
+    "latest": "2013.01.06", 
+    "signature": "72158cdba391628569ffdbea259afbcf279bbe3d8aeb7492690735dc1cfa6afa754f55c61196f3871d429599ab22f2667f1fec98865527b32632e7f4b3675a7ef0f0fbe084d359256ae4bba68f0d33854e531a70754712f244be71d4b92e664302aa99653ee4df19800d955b6c4149cd2b3f24288d6e4b40b16126e01f4c8ce6", 
+    "versions": {
+        "2013.01.02": {
+            "bin": [
+                "http://youtube-dl.org/downloads/2013.01.02/youtube-dl", 
+                "f5b502f8aaa77675c4884938b1e4871ebca2611813a0c0e74f60c0fbd6dcca6b"
+            ], 
+            "exe": [
+                "http://youtube-dl.org/downloads/2013.01.02/youtube-dl.exe", 
+                "75fa89d2ce297d102ff27675aa9d92545bbc91013f52ec52868c069f4f9f0422"
+            ], 
+            "tar": [
+                "http://youtube-dl.org/downloads/2013.01.02/youtube-dl-2013.01.02.tar.gz", 
+                "6a66d022ac8e1c13da284036288a133ec8dba003b7bd3a5179d0c0daca8c8196"
+            ]
+        }, 
+        "2013.01.06": {
+            "bin": [
+                "http://youtube-dl.org/downloads/2013.01.06/youtube-dl", 
+                "64b6ed8865735c6302e836d4d832577321b4519aa02640dc508580c1ee824049"
+            ], 
+            "exe": [
+                "http://youtube-dl.org/downloads/2013.01.06/youtube-dl.exe", 
+                "58609baf91e4389d36e3ba586e21dab882daaaee537e4448b1265392ae86ff84"
+            ], 
+            "tar": [
+                "http://youtube-dl.org/downloads/2013.01.06/youtube-dl-2013.01.06.tar.gz", 
+                "fe77ab20a95d980ed17a659aa67e371fdd4d656d19c4c7950e7b720b0c2f1a86"
+            ]
+        }
+    }
+}

youtube_dl/update.py

@@ -15,33 +15,17 @@
 
 
 def rsa_verify(message, signature, key):
-    from struct import pack
     from hashlib import sha256
-
     assert isinstance(message, bytes)
-    block_size = 0
-    n = key[0]
-    while n:
-        block_size += 1
-        n >>= 8
-    signature = pow(int(signature, 16), key[1], key[0])
-    raw_bytes = []
-    while signature:
-        raw_bytes.insert(0, pack("B", signature & 0xFF))
-        signature >>= 8
-    signature = (block_size - len(raw_bytes)) * b'\x00' + b''.join(raw_bytes)
-    if signature[0:2] != b'\x00\x01':
+    byte_size = (len(bin(key[0])) - 2 + 8 - 1) // 8
+    signature = ('%x' % pow(int(signature, 16), key[1], key[0])).encode()
+    signature = (byte_size * 2 - len(signature)) * b'0' + signature
+    asn1 = b'3031300d060960864801650304020105000420'
+    asn1 += sha256(message).hexdigest().encode()
+    if byte_size < len(asn1) // 2 + 11:
         return False
-    signature = signature[2:]
-    if b'\x00' not in signature:
-        return False
-    signature = signature[signature.index(b'\x00') + 1:]
-    if not signature.startswith(b'\x30\x31\x30\x0D\x06\x09\x60\x86\x48\x01\x65\x03\x04\x02\x01\x05\x00\x04\x20'):
-        return False
-    signature = signature[19:]
-    if signature != sha256(message).digest():
-        return False
-    return True
+    expected = b'0001' + (byte_size - len(asn1) // 2 - 3) * b'ff' + b'00' + asn1
+    return expected == signature
 
 
 def update_self(to_screen, verbose, opener):