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CVE-2016-1285: An error parsing input received by the rndc control channel can cause an assertion failure in sexpr.c or alist.c
Author: Michael McNally Reference Number: AA-01352 Views: 58331 Created: 2016-03-09 18:30 Last Updated: 2016-04-18 23:34 0 Rating/ Voters

Document Version:          
2.0
Posting date: 
09 March 2016
Program Impacted: 
BIND
Versions affected: 
9.2.0 -> 9.8.8, 9.9.0->9.9.8-P3, 9.9.3-S1->9.9.8-S5, 9.10.0->9.10.3-P3
Severity: 
High
Exploitable: 
Remotely (on systems which accept control channel input from remote addresses.)

Description:

Testing by ISC has uncovered a defect in control channel input handling which can cause named to exit due to an assertion failure in sexpr.c or alist.c when a malformed packet is sent to named's control channel (the interface which allows named to be controlled using the 'rndc" server control utility).

This assertion occurs before authentication but after network-address-based access controls have been applied.  Or in other words:  an attacker does not need to have a key or other authentication, but does need to be within the address list specified in the "controls" statement in named.conf which enables the control channel.  If no "controls" statement is present in named.conf, named still defaults to listening for control channel information on loopback addresses (127.0.0.1 and ::1) if the file rndc.key is present in the configuration directory and contains a valid key.

A search for similar problems revealed an associated defect in the rndc server control utility whereby a malformed response from the server could cause the rndc program to crash.  For completeness, it is being fixed at the same time even though this defect in the rndc utility is not in itself exploitable.

Impact:

All servers are vulnerable if they accept remote commands on the control channel.  Servers which are vulnerable can be stopped by an attacker sending the offending packet if the attacker is sending from a system listed within the address list specified in the "controls" statement (or from localhost if the control channel is using the default address list) resulting in denial of service to clients.

CVSS Score:  7.8

CVSS Vector:  (AV:N/AC:L/Au:N/C:N/I:N/A:C)

For more information on the Common Vulnerability Scoring System and to obtain your specific environmental score please visit: http://nvd.nist.gov/cvss.cfm?calculator&adv&version=2&vector=(AV:N/AC:L/Au:N/C:N/I:N/A:C)

Workarounds:

Restrict access to the control channel (by using the "controls" configuration statement in named.conf) to allow connection only from trusted systems.

Note that if no "controls" statement is present, named defaults to allowing control channel connections only from localhost (127.0.0.1 and ::1) if and only if the file rndc.key exists in the configuration directory and contains valid key syntax.  If rndc.key is not present and no "controls" statement is present in named.conf, named will not accept commands on the control channel.

Active exploits:

No known active exploits.

Solution:  Upgrade to the patched release most closely related to your current version of BIND.

  • BIND 9 version 9.9.8-P4
  • BIND 9 version 9.10.3-P4

BIND 9 Supported Preview edition is a feature preview version of BIND provided exclusively to eligible ISC Support customers.

  • BIND 9 version 9.9.8-S6

Document Revision History:

1.0 Advance Notification 02 March 2016
1.1 "Versions affected" and "Solution" text expanded to cover BIND 9 Supported Preview Edition, 03 March 2016
2.0 Public Disclosure.  09 March 2016

Related Documents:

See our BIND9 Security Vulnerability Matrix at https://kb.isc.org/article/AA-00913 for a complete listing of Security Vulnerabilities and versions affected.

If you'd like more information on ISC Subscription Support and Advance Security Notifications, please visit http://www.isc.org/support/.

Do you still have questions?  Questions regarding this advisory should go to security-officer@isc.orgTo report a new issue, please encrypt your message using security-officer@isc.org's PGP key which can be found here: https://www.isc.org/downloads/software-support-policy/openpgp-key/.  If you are unable to use encrypted email, you may also report new issues at: https://www.isc.org/community/report-bug/.

Note: ISC patches only currently supported versions. When possible we indicate EOL versions affected.  (For current information on which versions are actively supported, please see http://www.isc.org/downloads/). 

ISC Security Vulnerability Disclosure Policy:  Details of our current security advisory policy and practice can be found here: https://kb.isc.org/article/AA-00861/164/ISC-Software-Defect-and-Security-Vulnerability-Disclosure-Policy.html

This Knowledge Base article https://kb.isc.org/article/AA-01352 is the complete and official security advisory document.

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