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AUSCERT External Security Bulletin Redistribution
ESB-2021.1088.2
Multiple dnsmasq vulnerabilities CVE-2020-25684,
CVE-2020-25685, and CVE-2020-25686
14 September 2021
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AusCERT Security Bulletin Summary
---------------------------------
Product: F5OS
Publisher: F5 Networks
Operating System: Network Appliance
Impact/Access: Provide Misleading Information -- Remote/Unauthenticated
Reduced Security -- Remote/Unauthenticated
Resolution: Mitigation
CVE Names: CVE-2020-25686 CVE-2020-25685 CVE-2020-25684
Reference: ESB-2021.0987
ESB-2021.0864
ESB-2021.0699
ESB-2021.0283
Original Bulletin:
https://support.f5.com/csp/article/K98221124
Revision History: September 14 2021: Vendor updated versions known to be vulnerable
March 31 2021: Initial Release
- --------------------------BEGIN INCLUDED TEXT--------------------
K98221124: Multiple dnsmasq vulnerabilities CVE-2020-25684, CVE-2020-25685, and
CVE-2020-25686
Original Publication Date: 31 Mar, 2021
Latest Publication Date: 13 Sep, 2021
Security Advisory Description
o CVE-2020-25684
A flaw was found in dnsmasq before version 2.83. When getting a reply from
a forwarded query, dnsmasq checks in the forward.c:reply_query() if the
reply destination address/port is used by the pending forwarded queries.
However, it does not use the address/port to retrieve the exact forwarded
query, substantially reducing the number of attempts an attacker on the
network would have to perform to forge a reply and get it accepted by
dnsmasq. This issue contrasts with RFC5452, which specifies a query's
attributes that all must be used to match a reply. This flaw allows an
attacker to perform a DNS Cache Poisoning attack. If chained with
CVE-2020-25685 or CVE-2020-25686, the attack complexity of a successful
attack is reduced. The highest threat from this vulnerability is to data
integrity.
o CVE-2020-25685
A flaw was found in dnsmasq before version 2.83. When getting a reply from
a forwarded query, dnsmasq checks in forward.c:reply_query(), which is the
forwarded query that matches the reply, by only using a weak hash of the
query name. Due to the weak hash (CRC32 when dnsmasq is compiled without
DNSSEC, SHA-1 when it is) this flaw allows an off-path attacker to find
several different domains all having the same hash, substantially reducing
the number of attempts they would have to perform to forge a reply and get
it accepted by dnsmasq. This is in contrast with RFC5452, which specifies
that the query name is one of the attributes of a query that must be used
to match a reply. This flaw could be abused to perform a DNS Cache
Poisoning attack. If chained with CVE-2020-25684 the attack complexity of a
successful attack is reduced. The highest threat from this vulnerability is
to data integrity.
o CVE-2020-25686
A flaw was found in dnsmasq before version 2.83. When receiving a query,
dnsmasq does not check for an existing pending request for the same name
and forwards a new request. By default, a maximum of 150 pending queries
can be sent to upstream servers, so there can be at most 150 queries for
the same name. This flaw allows an off-path attacker on the network to
substantially reduce the number of attempts that it would have to perform
to forge a reply and have it accepted by dnsmasq. This issue is mentioned
in the "Birthday Attacks" section of RFC5452. If chained with
CVE-2020-25684, the attack complexity of a successful attack is reduced.
The highest threat from this vulnerability is to data integrity.
Impact
CVE-2020-25684
This flaw allows an attacker to perform a DNS Cache Poisoning attack. If
chained with CVE-2020-25685 or CVE-2020-25686, the attack complexity of a
successful attack is reduced. The highest threat from this vulnerability is to
data integrity. The attacker needs access to the mgmt network of the velocity
chassis to inject these invalid replies.
CVE-2020-25685
This flaw allows an attacker to perform a DNS Cache Poisoning attack. If
chained with CVE-2020-25684, the attack complexity of a successful attack is
reduced. The highest threat from this vulnerability is to data integrity. The
attacker needs access to the mgmt network of the velocity chassis to inject
these invalid replies.
CVE-2020-25686
This flaw allows an off-path attacker on the network to substantially reduce
the number of attempts to forge a reply and for dnsmasq to accept the reply.
RFC5452 mentions this issue in the Birthday Attacks section. If chained with
CVE-2020-25684, the attack complexity of a successful attack is reduced. The
highest threat from this vulnerability is to data integrity. The attacker needs
access to the mgmt network of the velocity chassis to inject these invalid
replies.
Security Advisory Status
F5 Product Development has assigned ID 989425 (F5OS) to this vulnerability.
To determine if your product and version have been evaluated for this
vulnerability, refer to the Applies to (see versions) box. To determine if your
release is known to be vulnerable, the components or features that are affected
by the vulnerability, and for information about releases, point releases, or
hotfixes that address the vulnerability, refer to the following table. For more
information about security advisory versioning, refer to K51812227:
Understanding security advisory versioning.
+------------+------+--------------+----------+----------+------+-------------+
| | |Versions known|Fixes | |CVSSv3|Vulnerable |
|Product |Branch|to be |introduced|Severity |score^|component or |
| | |vulnerable^1 |in | |2 |feature |
+------------+------+--------------+----------+----------+------+-------------+
| |16.x |None |Not | | | |
| | | |applicable| | | |
| +------+--------------+----------+ | | |
| |15.x |None |Not | | | |
| | | |applicable| | | |
| +------+--------------+----------+ | | |
| |14.x |None |Not | | | |
|BIG-IP (All | | |applicable|Not | | |
|modules) +------+--------------+----------+vulnerable|None |None |
| |13.x |None |Not | | | |
| | | |applicable| | | |
| +------+--------------+----------+ | | |
| |12.x |None |Not | | | |
| | | |applicable| | | |
| +------+--------------+----------+ | | |
| |11.x |None |Not | | | |
| | | |applicable| | | |
+------------+------+--------------+----------+----------+------+-------------+
| |8.x |None |Not | | | |
| | | |applicable| | | |
|BIG-IQ +------+--------------+----------+ | | |
|Centralized |7.x |None |Not |Not |None |None |
|Management | | |applicable|vulnerable| | |
| +------+--------------+----------+ | | |
| |6.x |None |Not | | | |
| | | |applicable| | | |
+------------+------+--------------+----------+----------+------+-------------+
|F5OS |1.x |1.0.0 - 1.1.4 |None |Medium |4.0 |dnsmasq |
+------------+------+--------------+----------+----------+------+-------------+
|Traffix SDC |5.x |None |Not |Not |None |None |
| | | |applicable|vulnerable| | |
+------------+------+--------------+----------+----------+------+-------------+
^1F5 only evaluates software versions that have not yet reached the End of
Technical Support (EoTS) phase of their lifecycle.
^2The CVSSv3 score link takes you to a resource outside of AskF5, and it is
possible that the document may be removed without our knowledge.
Recommended Actions
If you are running a version listed in the Versions known to be vulnerable
column, you can eliminate this vulnerability by installing a version listed in
the Fixes introduced in column. If the Fixes introduced in column does not list
a version for your branch, then no update candidate currently exists for that
branch and F5 recommends upgrading to a version with the fix (refer to the
table).
If the Fixes introduced in column lists a version prior to the one you are
running, in the same branch, then your version should have the fix.
Mitigation
To mitigate this vulnerability, do not configure DNS servers on the VELOS
chassis system.
Supplemental Information
o K41942608: Overview of AskF5 security advisory articles
o K4602: Overview of the F5 security vulnerability response policy
o K4918: Overview of the F5 critical issue hotfix policy
o K8986: F5 software lifecycle policy
o K9970: Subscribing to email notifications regarding F5 products
o K9957: Creating a custom RSS feed to view new and updated documents
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