New Vulnerability in F5

In F5 iRules, there is a security weakness that stems from the use of RESOLV in iRule:: the search command can affect traffic.

Tuesday, November 3, 2020, 8:38 GMT

Core files and restarts are created by the management microkernel (TMM). It is influenced by the following goods and versions: BIG-IP 16.0.0, 15.1.0.0

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             AUSCERT External Security Bulletin Redistribution
                               ESB-2020.3781
      F5 iRules 'RESOLV::lookup' command vulnerability CVE-2020-5941
                              3 November 2020
===========================================================================
        AusCERT Security Bulletin Summary
        ---------------------------------
Product:           BIG-IP Products
Publisher:         F5 Networks
Operating System:  Network Appliance
Impact/Access:     Denial of Service -- Remote/Unauthenticated
Resolution:        Patch/Upgrade
CVE Names:         CVE-2020-5941  
Original Bulletin: 
   https://support.f5.com/csp/article/K03125360
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K03125360: F5 iRules 'RESOLV::lookup' command vulnerability CVE-2020-5941
Security Advisory
Original Publication Date: 03 Nov, 2020
Security Advisory Description
Using the RESOLV::lookup command within an iRule may cause the Traffic
Management Microkernel (TMM) to generate a core file and restart. This issue
occurs when data exceeding the maximum limit of a host name passes to the
RESOLV::lookup command. (CVE-2020-5941)
Impact
The BIG-IP system may temporarily fail to process traffic as it recovers from
a TMM restart. If the BIG-IP system is configured for high availability (HA),
the system fails over to a peer system.
Security Advisory Status
F5 Product Development has assigned ID 876353 (BIG-IP) 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  |Fixes     |          |CVSSv3|Vulnerable    |
|Product        |Branch|known to  |introduced|Severity  |score^|component or  |
|               |      |be        |in        |          |1     |feature       |
|               |      |vulnerable|          |          |      |              |
+---------------+------+----------+----------+----------+------+--------------+
|               |16.x  |16.0.0    |16.0.1    |          |      |              |
|               +------+----------+----------+          |      |              |
|               |15.x  |15.1.0    |15.1.1    |          |      |              |
|               +------+----------+----------+          |      |              |
|BIG-IP (LTM,   |14.x  |None      |Not       |          |      |              |
|AAM, AFM,      |      |          |applicable|          |      |              |
|Analytics, APM,+------+----------+----------+          |      |iRules        |
|ASM, DNS, FPS, |13.x  |None      |Not       |High      |7.5   |RESOLV::lookup|
|GTM, Link      |      |          |applicable|          |      |command       |
|Controller,    +------+----------+----------+          |      |              |
|PEM)           |12.x  |None      |Not       |          |      |              |
|               |      |          |applicable|          |      |              |
|               +------+----------+----------+          |      |              |
|               |11.x  |None      |Not       |          |      |              |
|               |      |          |applicable|          |      |              |
+---------------+------+----------+----------+----------+------+--------------+
|               |7.x   |None      |Not       |          |      |              |
|               |      |          |applicable|          |      |              |
|BIG-IQ         +------+----------+----------+          |      |              |
|Centralized    |6.x   |None      |Not       |Not       |None  |None          |
|Management     |      |          |applicable|vulnerable|      |              |
|               +------+----------+----------+          |      |              |
|               |5.x   |None      |Not       |          |      |              |
|               |      |          |applicable|          |      |              |
+---------------+------+----------+----------+----------+------+--------------+
|Traffix SDC    |5.x   |None      |Not       |Not       |None  |None          |
|               |      |          |applicable|vulnerable|      |              |
+---------------+------+----------+----------+----------+------+--------------+
^1The CVSSv3 score link takes you to a resource outside of AskF5, and it is
possible that the document may be removed without our knowledge.
Security Advisory Recommended Actions
If you are running a version listed in the Versions known to be vulnerable
column, you can eliminate this vulnerability by upgrading to a version listed
in the Fixes introduced in column. If the table lists only an older version
than what you are currently running, or does not list a non-vulnerable version,
then no upgrade candidate currently exists.
Mitigation
To mitigate this vulnerability, you can validate all limits of untrusted data
passed into the RESOLV::lookup command in the affected iRule. F5 recommends
that you reject and not pass any string that has 254 or more characters to the
RESOLV::lookup command.
For example, the following sample displays the string length check in an iRule:
# this pseudo code shows a general way to check for the string length and handle failure.
# the main idea is to check string length before sending to resolv::lookup command.
when SOME_GENERAL_EVENT {
    set string_check [string tolower [HTTP::uri]]
    if {([string length $string_check] > 253)} {
        log local0. "Hostname Length Check FAIL"
        # HANDLE FAILURE
    }
    else {
        log local0. "Hostname Length Check PASS"
        # PROCEED TO resolv::lookup
    }
}
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 K9502: BIG-IP hotfix and point release matrix
  o K13123: Managing BIG-IP product hotfixes (11.x - 16.x)
  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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===========================================================================
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