Update: Security Hole in Kernel Allows Privilege Extensions

Nov 04, 2009

A null-pointer dereference in the Linux kernel allows local users to assume root privileges. Brad Spengler, who claims first discovery, announced that he will present a corresponding exploit during the course of the day.

Concurrent with Spengler's discovery in mid-October, Earl Chew likewise brought attention to the bug in an lkml.org blog. The bug affects all kernel versions in the 2.6 series and was fixed in the upcoming 2.6.32 RC. So far Red Hat is the only distro providing patches for what is now the CVE-2009-3547 advisory. Users of other distros can apply a workaround that sets the pointer to a value higher than zero, which prevents the exploit. Admins can enter

# cat /proc/sys/vm/mmap_min_addr

to read the current pointer value. If larger than zero, no action need be taken, otherwise use the command

# sysctl -w vm.mmap_min_addr="4096"

to set the value to 4096, for example. The value, however, is only good until the next reboot. To give it a more lasting value, users of Debian or its derivatives should use the following commands:

# echo "vm.mmap_min_addr = 4096" > /etc/sysctl.d/mmap_min_addr.conf
# /etc/init.d/procps restart

Users of openSUSE should use the following command instead:

# echo -e "\nvm.mmap_min_addr=4096\n" >> /etc/sysctl.conf

followed by a system reboot.

First indications are that Ubuntu/Kubuntu 9.10 are not affected by the bug, because the initial counter is set to 65535. However, subsequently installed programs such as Wine or Qemu will reset the counter to zero. First tests with Wine installations show this to be evident. The openSUSE distro is potentially the most vulnerable in that the initial counter is also set to zero.

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  • get root

    sudo -s
  • sudo echo

    You can't 'sudo echo > outputfile'. Then echo gets called with superuser privileges, but the actual output gets piped to outputfile with normal user privileges and fails.

    The correct way would be to either use 'sudo -i' or 'sudo su' to enter a true root shell, or to use tee.

    $ echo "vm.mmap_min_addr = 4096" | sudo tee /etc/sysctl.d/mmap_min_addr.conf

    Add the argument -a to tee to make it append the echoed line to the end of the file. Merely using tee like above will replace the file if it exists with the new content.
  • Article update

    Due to some formatting problems the commands have not been shown correctly as in the original article. The article has been updated. We apologize for the inconvinience!
  • wrong code

    Please, remove <br> from code

    echo "vm.mmap_min_addr = 4096" > /etc/sysctl.d/mmap_min_addr.conf<br>
    /etc/init.d/procps restart

    This tag doesn't allow to run commands in case of copy/paste in terminal.
  • If you have wine installed the instructions are a bit different

    Check if you have a file here:

    If so, modify the statement in there from:
    vm.mmap_min_addr = 0

    vm.mmap_min_addr = 1024
    vm.mmap_min_addr = 4096

    Then run:
    sudo /etc/init.d/procps restart

    Then check it with the cat:
    cat /proc/sys/vm/mmap_min_addr
  • Permanent fix in Ubuntu

    The permanent fix work in ubuntu but you need to get to a root terminal window:

    # sudo gnome-terminal

    Then enter the commands in this new terminal.
  • Ubuntu/Debian NON-EXPERTS: For a quick and easy WORKING fix.....

    Ubuntu/Debian non-admin, non-experts can go to:


    for well-written, working instructions.

    The article on THIS page was incredibly disappointing because it assumes expert Linux terminal command knowledge. I literally wasted half an hour of my existence trying to figure out what I was doing wrong. Went to the site above, cut/paste x 2, done.
  • sudo

    Martini1179, try "sudo -i" and then enter those commands.
  • ...and

    ...and I checked the value and it IS at zero. I have Wine installed.
  • Terminal commands DO NOT work in Ubuntu Jaunty

    The terminal commands for the more permanent don't work in Ubuntu Jaunty. Whatever I do, I get a "permission denied" error, sudo or no sudo. It doesn't even ask for a sudo password.
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