Full Disclosure mailing list archives
Re[2]: MS Windows Screensaver Privilege Escalation
From: 3APA3A <3APA3A () SECURITY NNOV RU>
Date: Fri, 26 Nov 2004 19:12:21 +0300
Dear Matt Andreko, Ability to boot machine from bootable to CD is not a problem of Windows security, it's more problem of physical security. To prevent your machine from booting from bootable CD reliably you can use certified BIOS versions (HP and IBM have few), special marks and devices like Dallas Lock, Secret Net, etc. --Friday, November 26, 2004, 6:42:34 PM, you wrote to 3APA3A () SECURITY NNOV RU: MA> Perhaps this is just an amateurish question, but what if I booted off of MA> a knoppix cd and replaced the current screensaver with my "specially MA> crafted" screensaver? Or using the bootdisk at MA> http://home.eunet.no/~pnordahl/ntpasswd/ to edit the registry value? MA> I know you may think that this is useless, since if you boot off the cd MA> or disk, you already have better access to the machine, however doing MA> this method gets you admin access WITHOUT changing the password, correct? MA> Again, perhaps I'm misunderstanding, but wouldn't this work, and still MA> show that the vulnerability in the screensaver code is valid, and needs MA> to be updated? It could allow someone to get local admin access to the MA> machine without changing the password. MA> 3APA3A wrote:
Dear Matthew Walker, Permissions for HKEY_USERS\Control Panel\Desktop allow modification to only members of Administrators and System. Power Users can install software, so they can replace any file in SYSTEM32 directory, including screensaver. It allows to trojan any system file (for example, one can replace winspool.exe with cmd.exe to obtain SYSTEM permissions). It's by design and it's documented. Just never assign users in Power Users group, as Microsoft recommends you. I see no security vulnerability here. --Wednesday, November 24, 2004, 8:36:14 PM, you wrote to full-disclosure () lists netsys com: MW> To Whom it May Concern; MW> The Original Post is http://www.securityfocus.com/bid/11711 MW> On Windows XP all releases, when you replace, or change the MW> screensaver displayed on the login screen with a specially crafted MW> version designed to execute programs, those programs are launched MW> under the SYSTEM SID, IE: they are given automatically the highest MW> access level avalible to Windows. This level is not accessible even MW> to administrators. MW> This flaw is important because while one would need Power User MW> privledges or above to change the Login Screensaver, by default, any MW> user with the exception of guest can replace the login screensaver MW> file with a modified version. In theory, any determined user could MW> execute ANYTHING with SYSTEM privledges. A similar flaw exists in MW> Win2K, but Microsoft has ignored it. MW> Sincerly; MW> Matt Walker MW> _______________________________________________ MW> Full-Disclosure - We believe in it. MW> Charter: http://lists.netsys.com/full-disclosure-charter.html
-- ~/ZARAZA Особую проблему составляет алкоголизм. (Лем) _______________________________________________ Full-Disclosure - We believe in it. Charter: http://lists.netsys.com/full-disclosure-charter.html
Current thread:
- MS Windows Screensaver Privilege Escalation Matthew Walker (Nov 24)
- RE: MS Windows Screensaver Privilege Escalation joe (Nov 24)
- RE: [in] MS Windows Screensaver Privilege Escalation Curt Purdy (Nov 24)
- Re: MS Windows Screensaver Privilege Escalation 3APA3A (Nov 25)
- Re: MS Windows Screensaver Privilege Escalation Matt Andreko (Nov 27)
- Re[2]: MS Windows Screensaver Privilege Escalation 3APA3A (Nov 27)
- Re: MS Windows Screensaver Privilege Escalation Matt Andreko (Nov 27)
- Re[2]: MS Windows Screensaver Privilege Escalation 3APA3A (Nov 27)
- Re: MS Windows Screensaver Privilege Escalation David Vincent (Nov 27)
- Re: MS Windows Screensaver Privilege Escalation Matt Andreko (Nov 27)
- Re: MS Windows Screensaver Privilege Escalation Pavel Kankovsky (Nov 28)
- Re: MS Windows Screensaver Privilege Escalation devis (Nov 28)
- Re: MS Windows Screensaver Privilege Escalation Nick FitzGerald (Nov 28)
- Re: MS Windows Screensaver Privilege Escalation Paul Schmehl (Nov 29)
- RE: MS Windows Screensaver Privilege Escalation Kovács László (Nov 29)
- <Possible follow-ups>
- RE: MS Windows Screensaver Privilege Escalation Stuart Fox (DSL AK) (Nov 24)
- Re[2]: MS Windows Screensaver Privilege Escalation 3APA3A (Nov 25)