dhclient has a stack overflow vulnerability which makes it
theoretically possible for a rogue DHCP server to execute arbitrary
commands as root on the affected system through stack return subversion.
Posting date: 14 Jul 2009
DHCP 4.1 (all versions), 4.0 (all versions), 3.1
(all versions), 3.0 (all versions), 2.0 (all versions)
While generating a subnet number from the server-supplied leased
address and subnet-mask 'dhclient' copies the information into a
field without verifying if the length of the information exceeds the
length of the field.
Theoretically this allows a rogue DHCP server to execute arbitrary
commands as root on the affected system through stack return
This attack has little to no risk for a client situated on a network
that is well defended, whereas clients that are roaming to
potentially hostile or ad-hoc networks can see this attack to pose a
Factors complicating any attack would be:
- The attacker would need to generate messages the client views as authentic.
The attacker would then need to develop their attack within a limited packet size.
- One option is for the attacker to present itself as a suitable
DHCPv4 server for a network, in essence operating as a rogue DHCPv4
- Another option would be to insert messages into the conversation
between the client and the authentic DHCPv4 server. To do this the
attacker needs to accurately guess the client's randomly chosen
16-bit transaction ID and insert the attack precisely between the
client's request and the valid DHCPv4 server's reply.
- Neither of these is likely on a well defended network but
clients that are roaming may find them, especially the first, a severe
- Support for DHCPv4 total packet size may be limited from 576 octets
through the link MTU size (no support for fragmentation) up to
64KB. Of this, the DHCPv4 option payload space is limited by the
space taken up by the BOOTP header space, excepting the FILE and
SNAME fields (which can be used in 'option overloading' to carry
option contents, such as the subnet-mask).
There is no known workaround, you must install the patches listed below to protect the DHCP client.
None known at this time
Upgrade to 4.1.0p1, 4.0.1p1, or 3.1.2p1
There are no fixes planned for DHCP 3.0 or DHCP 2.0, as those release trains have reached End-Of-Life.
Credit: Mandriva Linux Engineering Team and for discovering and reporting the software flaw.
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Note: ISC patches only currently supported versions. When possible we indicate EOL versions affected.
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This Knowledge Base article https://kb.isc.org/article/AA-00962 is the complete and official security advisory document.
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