From: Filippo Valsorda Date: Mon, 14 Dec 2015 02:18:13 +0000 (+0000) Subject: [update] fix (unexploitable) BB'06 vulnerability in rsa_verify X-Git-Url: http://git.oshgnacknak.de/?a=commitdiff_plain;h=4d318be1951d6bbae0eae7aff69a58de353c8337;p=youtube-dl [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. --- diff --git a/test/test_update.py b/test/test_update.py new file mode 100644 index 000000000..d9c71511d --- /dev/null +++ b/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() diff --git a/test/versions.json b/test/versions.json new file mode 100644 index 000000000..6cccc2259 --- /dev/null +++ b/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" + ] + } + } +} \ No newline at end of file diff --git a/youtube_dl/update.py b/youtube_dl/update.py index 995b8ed96..e4a1aaa64 100644 --- a/youtube_dl/update.py +++ b/youtube_dl/update.py @@ -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):