[Kea-announce] CVE-2019-6474: An oversight when validating incoming client requests can lead to a situation where the Kea server will exit when trying to restart

[Michael McNally]

CVE:                 CVE-2019-6474
Document Version:    2.0
Posting date:        28 August 2019
Program Impacted:    Kea DHCP
Versions affected:   1.4.0 -> 1.5.0. Versions prior to 1.4.0 are
                     considered "End of Life" and have not been tested
                     for this vulnerability, though they are believed to
                     be affected. Also affects development versions
1.6.0-beta1
                     and 1.6.0-beta2
Severity:            Medium

Exploitable:

   From adjacent networks permitted to relay DHCP traffic to the
   Kea server

Description:

   A missing check on incoming client requests can be exploited to
   cause a situation where the Kea server's lease storage contains
   leases which are rejected as invalid when the server tries to
   load leases from storage on restart. If the number of such leases
   exceeds a hard-coded limit in the Kea code, a server trying to
   restart will conclude that there is a problem with its lease
   store and give up.

Impact:

   Only Kea servers which use memfile storage for leases are affected
   by this vulnerability.

   An attacker can exploit the missing check to deliberately create
   a situation where the server will not restart properly should
   it stop for any reason.

CVSS Score:          5.7
CVSS Vector:         CVSS:3.0/AV:A/AC:L/PR:N/UI:R/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:A/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H

Workarounds:

   None.

Active exploits:

   No known active exploits

Solution:

   Upgrade to a version of Kea containing a fix, available via
https://www.isc.org/downloads.

   -  Kea 1.4.0-P2
   -  Kea 1.5.0-P1
   -  Kea 1.6.0

Document Revision History:

   1.0 Advance Notification, 21 August 2019
   2.0 Public Disclosure, 28 August 2019

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