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Bug#858373: apache2: segfaults upon recieving bad request when using worker/event mpm and cgid errordoc


First, thank you very much for the detailed bug report, very useful!
Responses inline.

On Tue, Mar 21, 2017 at 11:56:40AM -0500, Brian Kroth wrote:
> Package: apache2.2-common
> Version: 2.2.22-13+deb7u8
> Severity: normal
> Tags: security
> Dear Maintainer,
> We have some websites running on Debian Wheezy, so still using Apache
> 2.2.22, that are configured either in Worker or Event MPM (so are using
> mod_cgid in what follows), and have a custom "ErrorDocument 400" directive
> that points at a perl script for providing custom ModSecurity error.

Interesting. It would have been useful to see actual configuration
examples, as I had to go through a little bit of digging to reproduce
the issue. Just using cgid or worker is not sufficient - you actually
*do* need a ErrorDocument directive as well. So thanks to providing
those details, but snippets would have helped as well! :)
> I haven't dug up an older version of the package from snapshots to confirm
> this, but I think that since the recently backported HttpProtocolOptions
> directive to that version (BTW, where was that announced - I had to run
> strings on the binary to find it), I've been seeing a lot of
> segfault/coredumps registered in the Apache error logs.

I'm sorry to hear that. The change was announced in DLA-841-1 back in


If you haven't seen that announcement, you may not be subscribed to the
debian-lts-announce mailing list, in which case I strongly suggest you


There was also a lengthy discussion regarding the patchset on the
debian-lts mailing list:


Participation to the debian-lts mailing list is not mandatory for LTS
users, however...

> After some analysis, I've found that I can reproduce the error with a fairly
> trivial shell command:
> # echo -ne "GET / HTTP/1.0\n" | nc $some_website 80

This definitely looks like a heading parsing regression caused by
DLA-841-1. I cannot reproduce with a vanilla Apache install.

To reproduce, on wheezy:

 1. apt-get install apache2
 2. create a dummy perl script in /usr/lib/cgi-bin/hello.pl

        print "Content-type: text/html\n\n";
        print "Hello, World.";

 3. make it executable
 4. add this directive, say in /etc/apache2/conf.d/hello

        ErrorDocument 400 /cgi-bin/hello.pl

 5. reload apache (apache2ctl graceful or whatever)
 6. issue the killer request:

        echo -ne "GET / HTTP/1.0\n" | nc localhost 80

> > From the coredump, I was able to find that this line (1371) in the
> cgid_handler() code in the modules/generators/mod_cgid.c source file has a
> null pointer issue on the r->protocol field:
> 	is_included = !strcmp(r->protocol, "INCLUDED");
> Seems like a bit of a security issue to me.



On Tue, Apr 11, 2017 at 12:08:11PM +0930, Doran Moppert wrote:
> This looks like a form of CVE-2015-0253, which affected upstream apache
> 2.4.11, was introduced by the backport.  The fix is to ensure
> r->protocol is always populated:
> https://svn.apache.org/viewvc?view=revision&revision=1668879

Good findings. The fun part is that the above patch doesn't apply
because the protocol initialization was just missing. So this is
possibly broader than just 400 errors.

Note that I have tested this in jessie, and it doesn't seem affected, so
the backport for CVE-2016-8743 was done correctly there.

I'll prepare a package to fix this shortly.


Cyberspace. A consensual hallucination experienced daily by billions
of legitimate operators, in every nation, by children being taught
mathematical concepts...
                       - William Gibson

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