Bugtraq mailing list archives
答复: An alternative method to check LKM backdoor/rootkit
From: "Wang Jian" <lark () marsec net>
Date: Thu, 18 Apr 2002 10:59:46 +0800
-----原始邮件----- 发件人: Florian Weimer [mailto:Weimer () CERT Uni-Stuttgart DE] 发送时间: 2002年4月18日 06:05 收件人: Paul Starzetz 抄送: Wang Jian íõ½£ [±±¾©]; bugtraq () securityfocus com 主题: Re: An alternative method to check LKM backdoor/rootkit Paul Starzetz <paul () starzetz de> writes:Be sure that this will be fixed in the next 'generation' of LRKM's. Patching the device methods for disk special nodes is not abig deal -why not to incorporate even your code into one of the niceLRKM's? Youprobably found a weaknes of 'current' LRKM's but in generalit is a badidea to check your machine while running a compromised kernel.I agree. You can never be sure which kernel you are running. An attacker could have placed a modified kernel on a swap device (which excludes this very area from being used as swap space), and tweaked the boot loader to load the modified kernel.
If the file integrit check reveals that the boot loader is tweaked, the LKM loses the game in the first place, other tricks are just futile. Rewrite boot sector to a correct one will be enough for recovery. If it hide the hacked boot loader, then my code can reveal it unless it also intercept the raw disk io layer. This specific example is very simple to check and overcome. If you want to: 1. swapoff this device 2. dump it to a file 3. format it again 4. swapon it The LKMs can only continue the game by intercepting raw disk io.
Using this approach, the modified kernel image can be made completely invisible easily, and it still survives reboot. Such a modification is very hard to spot even during an offline analysis, and the checklists I've seen so far do not address this problem at all. -- Florian Weimer Weimer () CERT Uni-Stuttgart DE University of Stuttgart
http://CERT.Uni-Stuttgart.DE/people/fw/ RUS-CERT +49-711-685-5973/fax +49-711-685-5898
Current thread:
- An alternative method to check LKM backdoor/rootkit Wang Jian (Apr 16)
- Re: An alternative method to check LKM backdoor/rootkit Paul Starzetz (Apr 17)
- Re: An alternative method to check LKM backdoor/rootkit Florian Weimer (Apr 17)
- Re: An alternative method to check LKM backdoor/rootkit Karsten W. Rohrbach (Apr 18)
- 答复: An alternative method to check LKM backdoor/rootkit Wang Jian (Apr 18)
- Re: An alternative method to check LKM backdoor/rootkit Florian Weimer (Apr 17)
- <Possible follow-ups>
- RE: An alternative method to check LKM backdoor/rootkit Philippe Bourgeois (Apr 17)
- Re: An alternative method to check LKM backdoor/rootkit Paul Starzetz (Apr 17)