CVE-2018-5732: A specially constructed response from a malicious server can cause a buffer overflow in dhclient

[Michael McNally]

CVE:                 CVE-2018-5732
Document Version:    1.0
Posting date:        28 February 2018
Program Impacted:    DHCP
Versions affected:   4.1.0 -> 4.1-ESV-R15, 4.2.0 -> 4.2.8,
                     4.3.0 -> 4.3.6, 4.4.0
Severity:            High
Exploitable:         Remotely

Description:

   Failure to properly bounds check a buffer used for processing
   DHCP options allows a malicious server (or an entity masquerading
   as a server) to cause a buffer overflow (and resulting crash)
   in dhclient by sending a response containing a specially constructed
   options section.

Impact:

   Affected versions of dhclient should crash due to an out-of-bounds
   memory access if they receive and process a triggering response
   packet.  However, buffer overflow outcomes can vary by operating
   system and outcomes such as such as remote code execution may
   be possible in some circumstances.  Where they are present,
   operating system mitigation strategies such as address space
   layout randomization (ASLR) should make it difficult to leverage
   this vulnerability to achieve remote code execution but we can
   not rule it out as impossible.  The safest course is to patch
   dhclient so that the buffer overflow cannot occur.

CVSS Score:          7.5
CVSS Vector:         CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

For more information on the Common Vulnerability Scoring System and
to obtain your specific environmental score please visit:
https://www.first.org/cvss/calculator/3.0#CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Workarounds:         None.
Active exploits:     No known active exploits.

Solution:

   Upgrade to the patched release most closely related to your
   current version of DHCP.

   - DHCP 4.1-ESV-R15-P1
   - DHCP 4.3.6-P1
   - DHCP 4.4.1

Acknowledgements:

   ISC would like to thank Felix Wilhelm, Google Security Team, for
   reporting this vulnerability.

Document Revision History:

   1.0 Advance Notification 21 February 2018
   1.1 Strengthened language in "Impact" section 27 February 2018
   2.0 Public Disclosure 28 February 2018

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Note:

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   be found here: https://kb.isc.org/article/AA-00861

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