CVE-2018-5733: A malicious client can overflow a reference counter in ISC dhcpd

Michael McNally mcnally at
Wed Feb 28 17:19:40 UTC 2018

CVE:                 CVE-2018-5733
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:            Medium
Exploitable:         Remotely


   A malicious client which is allowed to send very large amounts
   of traffic (billions of packets) to a DHCP server can eventually
   overflow a 32-bit reference counter, potentially causing dhcpd
   to crash.


   Successful exploitation of this vulnerability may exhaust the
   memory available to dhcpd and/or cause it to crash, resulting
   in a denial of service to clients.

CVSS Score:          5.9
CVSS Vector:         CVSS:3.0/AV:N/AC:H/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:

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


   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


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

Document Revision History:

   1.0 Advance Notification 21 February 2018
   2.0 Public Disclosure 28 February 2018

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