A remote attacker can trigger the buffer overflow vulnerability to execute malicious code on affected Linux systems with just a malicious DNS response.

Chris Coulson, Ubuntu developer at Canonical, has found a critical vulnerability Linux that can be exploited to remotely hack machines running the popular OS. The flaw, tracked as CVE-2017-9445, resides in the Systemd init system and service manager for Linux operating systems.

A remote attacker can trigger the buffer overflow vulnerability to execute malicious code with just a malicious DNS response.

The expert has found the vulnerability in the ‘dns_packet_new‘ function of ‘systemd-resolved,’ that handles a DNS response and provides network name resolution to local applications. A specially crafted malicious DNS response can crash ‘systemd-resolved’ program remotely every time the system tries to lookup for a hostname on an attacker-controlled DNS service. The attacker can trigger the flaw by sending a large DNS response that triggers a buffer overflow that leads to remote code execution.

“Certain sizes passed to dns_packet_new can cause it to allocate a buffer that’s too small. A page-aligned number – sizeof(DnsPacket) + sizeof(iphdr) + sizeof(udphdr) will do this – so, on x86 this will be a page-aligned number – 80. Eg, calling dns_packet_new with a size of 4016 on x86 will result in an allocation of 4096 bytes, but 108 bytes of this are for the DnsPacket struct.” explains Coulson.

“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.”

The flaw affects the

The flaw affects the Systemd version 223, which is dated back June 2015, and later, including Systemd version 233 launched in March 2017.

The vulnerability affects the Ubuntu versions 17.04 and version 16.10; Debian versions Stretch (aka Debian 9), Buster (aka 10) and Sid (aka Unstable); and various other Linux distributions that use Systemd. Linux users and system administrators must update their installs as soon as possible.

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