[ISN] New Linux Security Hole Found

From: InfoSec News (isn@private)
Date: Mon Jun 14 2004 - 22:53:28 PDT

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    By Steven J. Vaughan-Nichols 
    June 14, 2004    
    A Linux bug was recently uncovered by a young Norwegian programmer
    that, when exploited by a simple C program, could crash most Linux 2.4
    or 2.6 distributions running on an x86 architecture.
    "Using this exploit to crash Linux systems requires the (ab)user to
    have shell access or other means of uploading and running the program
    - like cgi-bin and FTP access," reports the discoverer, Øyvind Sæther.
    "The program works on any normal user account, and root access is not
    required," Sæther reported. "This exploit has been reported used to
    take down several 'lame free-shell providers' servers. [Running code
    you know will damage a system intentionally and hacking in general] is
    illegal in most parts of the world and strongly discouraged."
    Along with the code needed to use the exploit, Sæther also posted
    several patches to 2.4 and 2.6 kernels that will keep the exploit from
    crashing systems.
    Several security problems have been uncovered in Linux over the past
    year. The most serious was uncovered in February by the Polish
    security nonprofit organization iSEC Security Research.
    The biggest of these security holes, called "Linux kernel do_mremap
    VMA limit local privilege escalation vulnerability" by iSEC, could
    have enabled a cracker to achieve full super-user and full
    administration privileges. In each case, fixes were quickly delivered
    by the Linux open-source community.
    This latest security hole, however, can be used to crash a system, but
    it doesn't give an attacker any other control of a Linux system.
    Technically, the problem exists because the Linux kernel's signal
    handler isn't handling floating-point (FP) exceptions correctly.  
    Linux's creator, Linus Torvalds, said, "There's a path into the kernel
    where if there is a pending FP error, the kernel will end up taking an
    FP exception, and it will continue to take the FP exception forever.  
    Torvalds already has the problem well in hand, he said. "I fixed it in
    my [source code] tree a few days ago, so it's in the current
    snapshots, and if I wasn't in the middle of a move [to Portland, Ore.]
    I'd have released a 2.6.7 already. As it is, I'll hopefully have it
    done by tomorrow [June 15].
    Eric Raymond, president of the Open Source Initiative, added, "It
    isn't a big deal. This one can be trivially fixed. This fixable kernel
    crasher doesn't cause any new problems."
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