title:  named exits with a REQUIRE assertion failure if it receives a null command string on its control channel
description: named contains a feature which allows operators to issue commands to a running server by communicating with the server process over a control channel, using a utility program such as rndc. A regression introduced in a recent feature change has created a situation under which some versions of named can be caused to exit with a REQUIRE assertion failure if they are sent a null command string. Affects BIND 9.9.9->9.9.9-P7, 9.9.10b1->9.9.10rc2, 9.10.4->9.10.4-P7, 9.10.5b1->9.10.5rc2, 9.11.0->9.11.0-P4, 9.11.1b1->9.11.1rc2, 9.9.9-S1->9.9.9-S9.
problem types: The BIND control channel is not configured by default, but when configured will accept commands from those IP addresses that are specified in its access control list and/or from clients which present the proper transaction key.  Using this defect, an attacker can cause a running server to stop if they can get it to accept control channel input from them.  In most instances this is not as bad as it sounds, because existing commands permitted over the control channel (i.e. "rndc stop") can already be given to cause the server to stop.
However, BIND 9.11.0 introduced a new option to allow "read only" commands over the command channel.  Using this restriction, a server can be configured to limit specified clients to giving control channel commands which return information only (e.g. "rndc status") without affecting the operational state of the server.  The defect described in this advisory, however, is not properly stopped by the "read only" restriction, in essence permitting a privilege escalation allowing a client which should only be permitted the limited set of "read only" operations to cause the server to stop execution.
affected:
{
product: BIND 9
vendor: ISC
versions:
status: affected, version: 9.9.9->9.9.9-P7, 9.9.10b1->9.9.10rc2, 9.10.4->9.10.4-P7, 9.10.5b1->9.10.5rc2, 9.11.0->9.11.0-P4, 9.11.1b1->9.11.1rc2, 9.9.9-S1->9.9.9-S9
}
metrics:
cvssV3_0: [
attackComplexity: LOW
attackVector: NETWORK
availabilityImpact: HIGH
baseScore: 6.5
baseSeverity: MEDIUM
confidentialityImpact: NONE
integrityImpact: NONE
privilegesRequired: LOW
scope: UNCHANGED
userInteraction: NONE
vectorString: CVSS:3.0/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
version: 3.0
]
solutions: Upgrade to the patched release most closely related to your current version of BIND. These can all be downloaded from http://www.isc.org/downloads.
BIND 9 version 9.9.9-P8
BIND 9 version 9.10.4-P8
BIND 9 version 9.11.0-P5
BIND Supported Preview Edition is a special feature preview branch of BIND provided to eligible ISC support customers.
BIND 9 version 9.9.9-S10
New maintenance releases of BIND are also scheduled which contain the fix for this vulnerability.  In addition to the security releases listed above, fixes for this vulnerability are also included in these release candidate versions:
BIND 9 version 9.9.10rc3
BIND 9 version 9.10.5rc3
BIND 9 version 9.11.1rc3
workarounds: None.  However, in a properly configured server, access to the control channel should already be limited by either network ACLs, TSIG keys, or both.