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Systemd flaw leaves many Linux distros open to attack

A flaw in systemd, the init system used on many Linux systems, can be exploited using a malicious DNS query to either crash a system or to run code remotely.

The vulnerability resides in the daemon systemd-resolved and can be triggered using a TCP payload, according to Ubuntu developer Chris Coulson.

This component can be tricked into allocating less memory than needed for a look-up. When the reply is bigger it overflows the buffer allowing an attacker to overwrite memory.

This would result in the process either crashing or it could allow for code execution remotely.

"A malicious DNS server can exploit this by responding with a specially crafted TCP payload to trick systemd-resolved in to allocating a buffer that's too small, and subsequently write arbitrary data beyond the end of it," is how Coulson put it.

The error was introduced into the systemd code in June 2015 in version 223.

Many Linux distributions have adopted systemd as their default init system but some have not yet moved from the old SysV init system.

Ubuntu has released patches for its two most recent releases — 16.10 and 17.04 — to fix the issue.

Debian is yet to issue a fix, but has pointed out that systemd-resolved is not enabled by default in its latest release, Stretch. Older Debian releases like Jessie and Wheezy do not contain the vulnerable code.

Red Hat said the flaw did not affect versions of systemd shipped with Red Hat Enterprise Linux 7.

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Sam Varghese

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A professional journalist with decades of experience, Sam for nine years used DOS and then Windows, which led him to start experimenting with GNU/Linux in 1998. Since then he has written widely about the use of both free and open source software, and the people behind the code. His personal blog is titled Irregular Expression.

 

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