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All,

Note: this was not a vote.

The consensus seems to be that SSIs should be moved into a separate
JAR file.

I've done a *very* short investigation, and I have discovered the
following:

1. Tomcat builds fine after removing the entire
org.apache.catalina.ssi source package, so it's completely isolated
from the rest of Tomcat (which was entirely expected). This suggests
that releasing Tomcat without any of the SSI components is practical
and relatively easy.

The stock conf/web.xml contains a sample configuration for the SSI
servlet. We will have to decide what to do with that. I can think of
at least two options:

  a. Remove it from the stock conf/web.xml entirely
  b. Add comments to conf/web.xml indicating that the SSI component is
a separate download

I think I like #2 better.

2. Separating the packaging should be easy. Note that I haven't
actually done this:

i.  Modify files.catalina in build.xml to <exclude> the
org.apache.catalina.ssi package
ii. Modify the "package" target in build.xml to <jarIt
jarfile="catalina-ssi.jar" .../> with the appropriate classes

I think this is super simple to do and we should go ahead and do this,
/now/. For embedded clients who don't care about SSI, this gives them
a JAR today that they can simply remove from their bundled clients to
save a little space.

3. The SSI component uses a bunch of internal(ish) Tomcat/Catalina
APIs. This may complicate fully-extracting the SSI component and
making it a standalone product (e.g. cross-container):

org.apache.catalina.connector.Connector;
org.apache.catalina.connector.Request;
org.apache.catalina.util.IOTools;
org.apache.catalina.util.Strftime;
org.apache.catalina.util.URLEncoder;
org.apache.coyote.Constants;
org.apache.tomcat.util.buf.B2CConverter;
org.apache.tomcat.util.buf.UDecoder;
org.apache.tomcat.util.http.FastHttpDateFormat;
org.apache.tomcat.util.http.RequestUtil;
org.apache.tomcat.util.res.StringManager;
org.apache.tomcat.util.security.Escape;

Some of them are simply for convenience -- e.g. UDecoder,
FastHttpDateFormat, etc. Those could easily be replaced with
alternatives or re-implementations. I haven't yet looked at how much
the org.apache.catalina.connector.Connector and
org.apache.catalina.connector.Request classes are used. It's possible
that these could be replaced with the generic versions of themselves
(e.g. HttpServletRequest and ... I'm not sure what we get from the
Connector but of course there is no direct replacement for that in the
public API).

So I'd like to move-forward with the separation of the SSI component
into a separate JAR file and then see what can be re-factored within
SSI itself to divorce it from internal Tomcat APIs.

- -chris

On 10/7/19 10:46, Christopher Schultz wrote:
> All,
> 
> I recently gave a presentation on locking-down Apache Tomcat[1] and
> I briefly discussed the "sharp edges" present in Tomcat. Some of
> them are unnecessarily sharp and may be actually unnecessary. I'm
> going to make a few proposals to remove functions from Tomcat.
> 
> Proposal: Remove Server-Side Includes
> 
> Justification:
> 
> The SSI module is a remote-code execution (RCE) vulnerability as a 
> feature. My sense is that SSI is a little-used feature. A few
> years ago, markt[2] asked if anyone was using SSI. The only replies
> were from other Tomcat devs commenting on what to do with SSI if
> it's no longer in the main Tomcat distribution; there were no
> community members who responded saying that SSI was important to
> them.
> 
> If the packaging of Tomcat could be tweaked a bit to move the SSI 
> components into a separate JAR file (e.g. move 
> org/apache/catalina/ssi/* to catalina-ssi.jar) and if the SSI 
> components don't rely on any Tomcat specific capabilities or 
> internals, then the cattalina-ssi.jar file could be used between 
> Tomcat versions. For example, a user of Tomcat 10 who still needs
> SSI could get the SSI module from a distribution of Tomcat 8.5.x or
> 9.x.
> 
> -chris
> 
> 
> [1]
> http://tomcat.apache.org/presentations.html#latest-locking-down-tomc
>
> 
at
> [2] 
> https://lists.apache.org/thread.html/969a9d1b6e883a4017907c44829288062
4c
>
> 
c85eb22c490b241dc9c88@%3Cusers.tomcat.apache.org%3E
> 
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