> This "garbage" is exactly what you allowed to add via crafted request
> (curl -H ... etc).  Why you want to allow so?

I don't want to. It was "allowed" until now, as X-Forwarded-For headers were not
deleted by the reverse proxy.

I still think that many people are using Debian and mod_rpaf, and are not
deleting these headers.
Won't you do anything for them ?

> > (so the request has two X-Forwarded-For headers when it arrives
> > on the web front end, one is malicious, one is correct from a trusted 
> > source).
> > 
> > A workaround could be stripping the previous X-Forwarded-For headers on the
> > reverse proxy, but it shouldn't be necessary.
> 
> Usually, you can just ignore X-Forwarded-For, provided by client.  This
> case covers typical simple frontend+backend setup.
> 
> Of course, this shouldn't be necessary - but it's a good idea to expose
> less headers for modification to client, right?

Agreed. Still, there's a bug, and this "solution" is - a "best practice" but - 
only a
workaround to this bug.

My point is: 

allright, we should all harden our setups, but:

  * many people don't and it shouldn't be necessary for Apache2 to keep running 

  * there are no words about it in the docs provided by Debian :

    /usr/share/doc/libapache2-mod-rpaf/README.Debian
  
      Module configuration is pretty simple, there are only two directives to
      set; RPAFenable and RPAFproxy_ips. With the later you can define which
      IP's are your frontend proxies that sends the correct X-Forwarded-For
      headers. If you do not use the RPAFproxy_ips directive then the module
      will not change the remote address of the incoming connection at any
      time.

  * The bug is exposed by the ipv6 patch which has been applied by Debian.
    I cannot reproduce the segfaults with upstream sources.
    There is likely to be an issue with upstream code, but the NULL pointer
    dereference has been introduced by Debian.

Cheers


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