[ASA-202006-13] bind: denial of service

[Morten Linderud]

Arch Linux Security Advisory ASA-202006-13
==========================================

Severity: Medium
Date    : 2020-06-28
CVE-ID  : CVE-2020-8618 CVE-2020-8619
Package : bind
Type    : denial of service
Remote  : Yes
Link    : https://security.archlinux.org/AVG-1191

Summary
=======

The package bind before version 9.16.4-1 is vulnerable to denial of
service.

Resolution
==========

Upgrade to 9.16.4-1.

# pacman -Syu "bind>=9.16.4-1"

The problems have been fixed upstream in version 9.16.4.

Workaround
==========

None.

Description
===========

- CVE-2020-8618 (denial of service)

An assertion check in BIND before 9.16.4 (that is meant to prevent
going beyond the end of a buffer when processing incoming data) can be
incorrectly triggered by a large response during zone transfer. An
attacker who is permitted to send zone data to a server via zone
transfer can exploit this to intentionally trigger the assertion
failure with a specially constructed zone, denying service to clients.

- CVE-2020-8619 (denial of service)

An issue has been found in Bind before 9.16.4, where an asterisk
character in an empty non-terminal can cause an assertion failure in
rbtdb.c.
The asterisk character ("*") is allowed in DNS zone files, where it is
most commonly present as a wildcard at a terminal node of the Domain
Name System graph. However, the RFCs do not require and BIND does not
enforce that an asterisk character be present only at a terminal node.
A problem can occur when an asterisk is present in an empty non-
terminal location within the DNS graph. If such a node exists, after a
series of queries, named can reach an inconsistent state that results
in the failure of an assertion check in rbtdb.c, followed by the
program exiting due to the assertion failure.
Unless a nameserver is providing authoritative service for one or more
zones and at least one zone contains an empty non-terminal entry
containing an asterisk ("*") character, this defect cannot be
encountered. A would-be attacker who is allowed to change zone content
could theoretically introduce such a record in order to exploit this
condition to cause denial of service, though we consider the use of
this vector unlikely because any such attack would require a
significant privilege level and be easily traceable.

Impact
======

A remote attacker with enough privileges to update a zone might be able
to crash a server via a crafted zone transfer or by inserting an
asterisk at a terminal node of a zone.

References
==========

https://downloads.isc.org/isc/bind9/9.16.4/doc/arm/html/notes.html#notes-for-bind-9-16-4
https://kb.isc.org/docs/cve-2020-8618
https://gitlab.isc.org/isc-projects/bind9/-/issues/1850
https://kb.isc.org/docs/cve-2020-8619
https://gitlab.isc.org/isc-projects/bind9/-/issues/1718
https://gitlab.isc.org/isc-projects/bind9/-/commit/569cc155b8680d8ed12db1fabbe20947db24a0f9
https://security.archlinux.org/CVE-2020-8618
https://security.archlinux.org/CVE-2020-8619
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