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AUSCERT External Security Bulletin Redistribution
ESB-2019.0280
K21942600: A virtual server with a Client SSL profile may
accept non-SSL traffic
31 January 2019
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AusCERT Security Bulletin Summary
---------------------------------
Product: F5 BIG-IP
Publisher: F5 Networks
Operating System: Network Appliance
Impact/Access: Unauthorised Access -- Remote/Unauthenticated
Resolution: Patch/Upgrade
Original Bulletin:
https://support.f5.com/csp/article/K21942600
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K21942600: A virtual server with a Client SSL profile may accept non-SSL
traffic
Security Advisory
Original Publication Date: Jan 30, 2019
Applies to (see versions):
o Product: BIG-IP
o 13.1.1, 13.1.0, 13.0.1, 13.0.0
Security Advisory Description
A Client SSL profile using a cipher group and an option that modifies supported
ciphers (for example no-dtls or no-ssl) accepts plain text connections, in
addition to correctly handling SSL traffic.
This issue occurs when all of the following conditions are met:
o A virtual server is configured with a Client SSL profile.
o The Client SSL profile is configured to use a cipher group.
o The Client SSL profile is also configured to modify the supported ciphers
with an option enabled, such as No SSL, No TLS, or No DTLS.
Important: The cipher group option was introduced in BIG-IP 13.0.0. Previous
versions are not affected by this issue.
Impact
This behavior allows information normally sent over encrypted channels to be
delivered over a clear text link. If client authentication is configured, clear
text requests are successful, allowing an unauthenticated client to access
resources that would otherwise require a valid client certificate.
Symptoms
As a result of this issue, you may encounter the following symptom:
o An affected virtual server may process non-SSL (clear text) requests.
Security Advisory Status
F5 Product Development has assigned ID 743857 to this issue. F5 has confirmed
that this issue exists in the products listed in the Applies to (see versions)
box, located in the upper-right corner of this article. For information about
releases, point releases, or hotfixes that resolve this issue, refer to the
following table.
+------------------+-----------------+----------------------------------------+
|Type of fix |Fixes introduced |Related articles |
| |in | |
+------------------+-----------------+----------------------------------------+
|Release |None |None |
+------------------+-----------------+----------------------------------------+
|Point release/ |13.1.1.4 |K9502: BIG-IP hotfix and point release |
|hotfix | |matrix |
+------------------+-----------------+----------------------------------------+
Security Advisory Recommended Actions
Workaround
To work around this issue, you can configure the affected Client SSL profile to
use a cipher suite and specify a cipher string with the desired ciphers, rather
than the Cipher Group and Options.. To do so, perform the following procedure:
Impact of workaround: The impact of the suggested workaround will depend on the
specific environment. F5 recommends testing any such changes during a
maintenance window with consideration to the possible impact on your specific
environment.
1. Log in to the Configuration utility.
2. Navigate to Local Traffic > Virtual Severs > Profiles > SSL > Client.
3. Select the affected Client SSL profile.
4. From the Configuration menu, select Advanced
5. In the Ciphers section, select Cipher Suites and enter the desired cipher
string in the text field.
6. Click Update.
Supplemental Information
o K51812227: Understanding Security Advisory versioning
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 K9502: BIG-IP hotfix and point release matrix
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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