CVE: CVE-2019-6477
Document version: 1.1
Posting date: 20 November 2019
Program impacted: BIND
Versions affected: BIND 9.11.6-P1 -> 9.11.12, 9.12.4-P1 -> 9.12.4-P2,
9.14.1 -> 9.14.7, and versions 9.11.5-S6 ->
9.11.12-S1 of BIND 9 Supported Preview Edition.
Versions 9.15.0 -> 9.15.5 of the BIND 9.15
development branch are also affected. Versions
prior to BIND 9.11.0 have not been evaluated for
vulnerability to CVE-2019-6477.
Severity: Medium
Exploitable: Remotely
Description:
By design, BIND is intended to limit the number of TCP clients that
can be connected at any given time. The update to this
functionality introduced by CVE-2018-5743 changed how BIND
calculates the number of concurrent TCP clients from counting the
outstanding TCP queries to counting the TCP client connections. On
a server with TCP-pipelining capability, it is possible for one TCP
client to send a large number of DNS requests over a single
connection. Each outstanding query will be handled internally as an
independent client request, thus bypassing the new TCP clients
limit.
Impact:
With pipelining enabled each incoming query on a TCP connection
requires a similar resource allocation to a query received via UDP
or via TCP without pipelining enabled. A client using a
TCP-pipelined connection to a server could consume more resources
than the server has been provisioned to handle. When a TCP
connection with a large number of pipelined queries is closed, the
load on the server releasing these multiple resources can cause it
to become unresponsive, even for queries that can be answered
authoritatively or from cache. (This is most likely to be perceived
as an intermittent server problem).
CVSS Score: 6.5
CVSS Vector: CVSS:3.1AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H/E:U/RL:O/RC:C