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             AUSCERT External Security Bulletin Redistribution

                    Netty vulnerability CVE-2021-21295
                              5 October 2021


        AusCERT Security Bulletin Summary

Product:           F5 BIG-IQ Centralized Management
Publisher:         F5 Networks
Operating System:  Network Appliance
Impact/Access:     Provide Misleading Information -- Existing Account
                   Reduced Security               -- Existing Account
Resolution:        None
CVE Names:         CVE-2021-21295  

Reference:         ESB-2021.3256

Original Bulletin: 

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K55834441: Netty vulnerability CVE-2021-21295

Original Publication Date: 02 Oct, 2021

Security Advisory Description

Netty is an open-source, asynchronous event-driven network application
framework for rapid development of maintainable high performance protocol
servers & clients. In Netty (io.netty:netty-codec-http2) before version
4.1.60.Final there is a vulnerability that enables request smuggling. If a
Content-Length header is present in the original HTTP/2 request, the field is
not validated by `Http2MultiplexHandler` as it is propagated up. This is fine
as long as the request is not proxied through as HTTP/1.1. If the request comes
in as an HTTP/2 stream, gets converted into the HTTP/1.1 domain objects
(`HttpRequest`, `HttpContent`, etc.) via `Http2StreamFrameToHttpObjectCodec
`and then sent up to the child channel's pipeline and proxied through a remote
peer as HTTP/1.1 this may result in request smuggling. In a proxy case, users
may assume the content-length is validated somehow, which is not the case. If
the request is forwarded to a backend channel that is a HTTP/1.1 connection,
the Content-Length now has meaning and needs to be checked. An attacker can
smuggle requests inside the body as it gets downgraded from HTTP/2 to HTTP/1.1.
For an example attack refer to the linked GitHub Advisory. Users are only
affected if all of this is true: `HTTP2MultiplexCodec` or `Http2FrameCodec` is
used, `Http2StreamFrameToHttpObjectCodec` is used to convert to HTTP/1.1
objects, and these HTTP/1.1 objects are forwarded to another remote peer. This
has been patched in 4.1.60.Final As a workaround, the user can do the
validation by themselves by implementing a custom `ChannelInboundHandler` that
is put in the `ChannelPipeline` behind `Http2StreamFrameToHttpObjectCodec`. (


This vulnerability may result in HTTP request smuggling. When malformed or
abnormal HTTP requests are interpreted by one or more entities in the data flow
between the user and the web server, such as a proxy or firewall, they can be
interpreted inconsistently, allowing the attacker to "smuggle" a request to one
device without the other device being aware of it.

Security Advisory Status

F5 Product Development has assigned ID 1046909 (BIG-IQ) 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.

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, the fix also applies to, 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   |Fixes     |          |CVSSv3|                            |
|Product    |Branch|known to be|introduced|Severity  |score^|Vulnerable component or     |
|           |      |vulnerable^|in        |          |2     |feature                     |
|           |      |1          |          |          |      |                            |
|           |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   |8.0.0 -    |None      |          |      |                            |
|           |      |8.1.0      |          |          |      |                            |
|BIG-IQ     +------+-----------+----------+          |      |Netty                       |
|Centralized|7.x   |7.0.0 -    |None      |Medium    |5.3   |(io.netty:netty-codec-http2)|
|Management |      |7.1.0      |          |          |      |                            |
|           +------+-----------+----------+          |      |                            |
|           |6.x   |6.1.0      |None      |          |      |                            |
|F5OS       |1.x   |None       |Not       |Not       |None  |None                        |
|           |      |           |applicable|vulnerable|      |                            |
|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

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.



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 K15106: Managing BIG-IQ product hotfixes
  o K15113: BIG-IQ 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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