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AUSCERT External Security Bulletin Redistribution
ESB-2022.2508
K08832573: DHCP vulnerability CVE-2021-25217
23 May 2022
===========================================================================
AusCERT Security Bulletin Summary
---------------------------------
Product: BIG-IP (all modules)
BIG-IQ Centralized Management
F5OS
Publisher: F5 Networks
Operating System: Network Appliance
Resolution: Mitigation
CVE Names: CVE-2021-25217
Original Bulletin:
https://support.f5.com/csp/article/K08832573
Comment: CVSS (Max): 8.8 CVE-2021-25217 (CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H)
CVSS Source: F5 Networks
Calculator: https://www.first.org/cvss/calculator/3.1#CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
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K08832573: DHCP vulnerability CVE-2021-25217
Original Publication Date: 21 May, 2022
Security Advisory Description
In ISC DHCP 4.1-ESV-R1 -> 4.1-ESV-R16, ISC DHCP 4.4.0 -> 4.4.2 (Other branches
of ISC DHCP (i.e., releases in the 4.0.x series or lower and releases in the
4.3.x series) are beyond their End-of-Life (EOL) and no longer supported by
ISC. From inspection it is clear that the defect is also present in releases
from those series, but they have not been officially tested for the
vulnerability), The outcome of encountering the defect while reading a lease
that will trigger it varies, according to: the component being affected (i.e.,
dhclient or dhcpd) whether the package was built as a 32-bit or 64-bit binary
whether the compiler flag -fstack-protection-strong was used when compiling In
dhclient, ISC has not successfully reproduced the error on a 64-bit system.
However, on a 32-bit system it is possible to cause dhclient to crash when
reading an improper lease, which could cause network connectivity problems for
an affected system due to the absence of a running DHCP client process. In
dhcpd, when run in DHCPv4 or DHCPv6 mode: if the dhcpd server binary was built
for a 32-bit architecture AND the -fstack-protection-strong flag was specified
to the compiler, dhcpd may exit while parsing a lease file containing an
objectionable lease, resulting in lack of service to clients. Additionally, the
offending lease and the lease immediately following it in the lease database
may be improperly deleted. if the dhcpd server binary was built for a 64-bit
architecture OR if the -fstack-protection-strong compiler flag was NOT
specified, the crash will not occur, but it is possible for the offending lease
and the lease which immediately followed it to be improperly deleted. (
CVE-2021-25217)
Impact
A stack-based buffer can overflow when statements are parsed with
colon-separated hex digits in config or lease files in dhcpd and dhclient.
Security Advisory Status
F5 Product Development has assigned ID 1102881 (BIG-IP and BIG-IQ) and ID
1106925 (F5OS-A and F5OS-C) to this vulnerability. This issue has been
classified as CWE-119: Improper Restriction of Operations within the Bounds of
a Memory Buffer.
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.
Note: After a fix is introduced for a given minor branch, that fix applies to
all subsequent maintenance and point releases for that branch, and no
additional fixes for that branch will be listed in the table. For example, when
a fix is introduced in 14.1.2.3, the fix also applies to 14.1.2.4, and all
later 14.1.x releases (14.1.3.x., 14.1.4.x). For more information, refer to
K51812227: Understanding security advisory versioning. Additionally, software
versions preceding those listed in the Applies to (see versions) box of this
article have reached the End of Technical Support (EoTS) phase of their
lifecycle and are no longer evaluated for security issues. For more
information, refer to the Security hotfixes section of K4602: Overview of the
F5 security vulnerability response policy.
+------------+------+--------------+----------+----------+------+-------------+
| | |Versions known|Fixes | |CVSSv3|Vulnerable |
|Product |Branch|to be |introduced|Severity |score^|component or |
| | |vulnerable^1 |in | |2 |feature |
+------------+------+--------------+----------+----------+------+-------------+
| |17.x |17.0.0 |None | | | |
| +------+--------------+----------+ | | |
| |16.x |16.1.0 - |None | | | |
| | |16.1.2 | | | | |
| +------+--------------+----------+ | | |
|BIG-IP (all |15.x |15.1.0 - |None | | |dhcp/dhclient|
|modules) | |15.1.5 | |High |8.8 |DHCP Relay |
| +------+--------------+----------+ | |Agent |
| |14.x |14.1.0 - |None | | | |
| | |14.1.4 | | | | |
| +------+--------------+----------+ | | |
| |13.x |13.1.0 - |None | | | |
| | |13.1.5 | | | | |
+------------+------+--------------+----------+----------+------+-------------+
|BIG-IQ |8.x |8.0.0 - 8.2.0 |None | | | |
|Centralized +------+--------------+----------+High |8.8 |dhcp/dhclient|
|Management |7.x |7.0.0 - 7.1.0 |None | | | |
+------------+------+--------------+----------+----------+------+-------------+
|F5OS-A |1.x |1.0.0 - 1.0.1 |None |High |8.8 |dhcp/dhclient|
+------------+------+--------------+----------+----------+------+-------------+
| | |1.3.0 - 1.3.2 | | | | |
|F5OS-C |1.x |1.2.0 - 1.2.2 |None |High |8.8 |dhcp/dhclient|
| | |1.1.0 - 1.1.4 | | | | |
+------------+------+--------------+----------+----------+------+-------------+
|Traffix SDC |5.x |None |Not |Not |None |None |
| | | |applicable|vulnerable| | |
+------------+------+--------------+----------+----------+------+-------------+
^1F5 evaluates only 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
Use static Management IP address
To mitigate this vulnerability, you can use a static Management IP address. For
more information, refer to K15040: Configuring and displaying the management IP
address for the BIG-IP system and K41712190: Displaying the management IP
address for the BIG-IQ system.
Protect the Management interface with Network Controls
You should restrict management access to only trusted users and devices over a
secure network. For more information about securing access to BIG-IP or
BIG-IQ systems, refer to the following articles:
o K13092: Overview of securing access to the BIG-IP system
o K46122561: Restricting access to the management interface using network
firewall rules
o K92748202: Restricting access to the BIG-IQ management interface using
network firewall rules
o K69354049: Restricting access to the BIG-IP management interface for
Configuration Utility and iControl REST services using iptables
Note: For BIG-IQ 7.x, secure the management interface by using an external
packet filtering device such as the BIG-IP Advanced Firewall Manager (AFM).
Disable DHCP Relay Agent (BIG-IP only)
If you configure the BIG-IP system as a DHCP Relay Agent, you should disable
it. For more information about configuring the BIG-IP system as a DHCP Relay
Agent, refer to the Configuring the BIG-IP System as a DHCP Relay Agent chapter
of the BIG-IP Local Traffic Manager: Implementations guide.
Note: For information about how to locate F5 product manuals, refer to
K98133564: Tips for searching AskF5 and finding product documentation.
Supplemental Information
o K41942608: Overview of 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 K9502: BIG-IP hotfix and point release matrix
o K13123: Managing BIG-IP product hotfixes (11.x - 17.x)
o K15106: Managing BIG-IQ product hotfixes
o K15113: BIG-IQ hotfix and point release matrix
o K48955220: Installing an OPSWAT Endpoint Security update on BIG-IP APM
systems (11.4.x and later)
o K167: Downloading software and firmware from F5
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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The University of Queensland
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