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NT vulnerable to attack on CPU

> http://www.pcweek.com/news/1216/18ent.html
>    December 18, 1996 5:45 PM ET
>    _NT vulnerable to attack on CPU_
>    _By Eamonn Sullivan_
>      Errors in the way Windows NT schedules concurrently running
>    applications leave it vulnerable to a simple, but very effective,
>    denial of service attack, according to a Windows NT expert.
>    "This is a wide-open hole just waiting for exploitation by an ActiveX
>    control," said Mark Russinovich, a consulting associate with Open
>    Systems Resources Inc. who discovered the vulnerability this week. The
>    flaw is particularly serious, since it can be easily exploited by an
>    ActiveX control or by a Netscape plug-in.
>    Russinovich wrote a simple utility that, while running with no special
>    security privileges, is able to take complete control of any Windows
>    NT server or workstation, rendering it useless for any other
>    applications. The algorithm used by Windows NT to protect itself
>    against such CPU-hogging attacks appears to be seriously flawed and
>    ineffective, Russinovich said.
>    The source code for the utility, which is called CpuHog, is available
>    on the Web at www.ntinternals.com.
>    _How it works_
>    Basically, Russinovich's program exploits a vulnerability in the way
>    Windows NT schedules the execution of processes.
>    Applications can set their own priority level, which affects how often
>    Windows NT allows those applications to run. An application running
>    under a user account with administrative privileges can set its
>    priority to any of 32 levels, with the highest level giving it more
>    time slices. Applications running under accounts without
>    administrative privileges can set their priority to any of the first
>    16 of those levels.
>    CpuHog sets its priority to the highest level available, which is
>    level 16 when run by a normal user. Windows NT attempts to deal with
>    CPU-hogging applications by boosting the priority of other
>    applications. However, Russinovich found that Windows NT will only
>    boost applications as high as level 15. Thus, all other applications -
>    even system utilities such as Task Manager - never get a chance to
>    execute while CpuHog is running.
>    PC Week Labs was able to duplicate Russinovich's findings. When run on
>    Windows NT 4.0, for example, the only way to regain control once
>    CpuHog was executed was to reset the PC.
>    _Old problem _
>    Hogging the CPU is one of the oldest known forms of denial of service
>    attack. So old, in fact, that many operating systems have developed a
>    defense. Many forms of Unix allow administrators to set limits on CPU
>    usage by user - limiting any one user to 50 percent of available CPU
>    cycles, for example.
>    Almost all forms of Unix also automatically decrease the priority of
>    the highest-priority processes when applications become starved for
>    CPU time, which is the opposite of what Windows NT does.
>    Russinovich said Microsoft could get around the problem fairly easily
>    in one of two ways: Either increase the maximum priority given to
>    other, CPU-starved applications above level 15, or increase the
>    priority of the Task Manager above level 16, so that it can be used to
>    end CPU-hogging applications.
>    Microsoft officials contacted for this story did not have a comment,
>    other than to say they are researching the problem.
>    [LINK]
>    _Copyright(c) 1996 Ziff-Davis Publishing Company. All rights reserved.
>    Reproduction in whole or in part in any form or medium without express
>    written permission of Ziff-Davis Publishing Company is prohibited. PC
>    Week and the PC Week logo are trademarks of Ziff-Davis Publishing
>    Company. PC Week Online and the PC Week Online logo are trademarks of
>    Ziff-Davis Publishing Company._
>     _Send mail to PC Week_



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