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

The rsa_verify code was vulnerable to a BB'06 attack, allowing to forge
signatures for arbitrary messages if and only if the public key exponent is
3.  Since the updates key is hardcoded to 65537, there is no risk for
youtube-dl, but I don't want vulnerable code in the wild.

The new function adopts a way safer approach of encoding-and-comparing to
replace the dangerous parsing code.
pull/8142/head
Filippo Valsorda 5 years ago
parent
commit
4d318be195
3 changed files with 72 additions and 24 deletions
  1. +30
    -0
      test/test_update.py
  2. +34
    -0
      test/versions.json
  3. +8
    -24
      youtube_dl/update.py

+ 30
- 0
test/test_update.py View File

@ -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()

+ 34
- 0
test/versions.json View File

@ -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"
]
}
}
}

+ 8
- 24
youtube_dl/update.py View File

@ -15,33 +15,17 @@ from .version import __version__
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':
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():
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
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):


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