1. Redhat Explains Why Chroot Is Not a Security Feature

    August 07, 2013

    I came across this Redhat security blog post that explains why the chroot command has it's uses, but it isn't magic security pixie dust. Running an application from within a chrooted jail or just on a well-configured system would result in the same level of security.

    Josh Bressers:

    Putting a regular user in a chroot() will prevent them from having access to the rest of the system. This means using a chroot is not less secure, but it is not more secure either. If you have proper permissions configured on your system, you are no safer inside a chroot than relying on system permissions to keep a user in check. Of course you can make the argument that everyone makes mistakes, so running inside a chroot is safer than running outside of one where something is going to be misconfigured. This argument is possibly true, but note that setting up a chroot can be far more complex than configuring a system. Configuration mistakes could lead to the chroot environment being less secure than non-chroot environments.

    In the past I've tried to setup a chroot for an application and it was a pain. If you want to do it well, it will take quite some effort and every application has it's own requirements. But why spend all this effort?

    Josh continues:

    it may not be possible to break out of the chroot, but the attacker can still use system resources, such as for sending spam, gaining local network access, joining the system to a botnet, and so on.

    A chroot jail hides the rest of the 'real' file system. But the file system is just one part of the security equation: an attacker that compromised the chrooted application can still execute arbitrary code. Not as the root user, fair enough, but does it really hinder the attacker? The attacker already gained a stepping stone to pivot into the rest of the network1. As a non-privileged user, the attacker can try to exploit local kernel vulnerabilities to gain root access or stage attacks through the network on other hosts.

    If you run some kind of forum or bulletin board, it is probably more likely that this software will be compromised than the web server itself. And the result is often the same: arbitrary code execution with the privileges of the web server software. So the attacker controls the application and thus all it's content, including email addresses and password(hashes).

    A chrooted jail does not provide any additional security in this scenario. It may be a bit more difficult to access the rest of the file system, but if the attacker has access as an unprivileged user and file system permissions are set properly, is there a benefit?

    I believe it is more wise to invest your time configuring proper file system privileges and propagate them through puppet, chef or ansible. And run some scripts to audit/validate file system privileges.

    Update

    If applications support chroot, it might still be wise to enable it. It's often very easy to configure and it will probably delay an attacker.


    1. If you implemented network segmentation properly and have a sane firewall, the impact could be limited. 

    Tagged as : Security Chroot

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