Bug#1081266: apache2: Reverse proxy via mod_rewrite broken after upgrade to 2.4.62-1~deb12u1

[Salvatore Bonaccorso <carnil@debian.org>]

Hi,

On Tue, Sep 10, 2024 at 06:59:51AM +0000, Markus Wollny wrote:
> Package: apache2
> Version: 2.4.62-1~deb12u1
> Severity: important
> X-Debbugs-Cc: markus.wollny@computec.de, team@security.debian.org
> 
> Dear Maintainer,
> 
> After upgrading apache2 packages, we noticed that our SEO rewriting rules in apache2 no longer worked and Tomcat tried to access non-existing file paths with URL encoded questionmarks.
> 
> I have first noticed that is issue affects Debian 12, but I can confirm that it also affects Debian 11, so this happens in oldstable, apache2 2.4.62-1~deb11u1, too.
> 
> To show the issue, you'll want to enable the following mods:
> a2enmod lbmethod_byrequests proxy proxy_ajp proxy_balancer slotmem_shm rewrite
> 
> I have set up a balancer worker in mods-available/proxy_balancer.conf:
> <Proxy balancer://tomcat>
>         BalancerMember ajp://localhost:8009 secret=youllneverknow
> </Proxy>
> 
> I have narrowed the issue down to using a proxy RewriteRule inside a Directory block. So to reproduce, set up /etc/apache2/sites-available/000-default.conf like this:
> 
> <VirtualHost *:80>
>         ServerAdmin webmaster@localhost
>         DocumentRoot /var/www/html
> 
>         ErrorLog ${APACHE_LOG_DIR}/error.log
>         CustomLog ${APACHE_LOG_DIR}/access.log combined
> 
>         <Directory "/var/www/html">
>                 DirectoryIndex index.html
>                 RewriteEngine On
>                 RewriteRule ^/?(.*?)$ balancer://tomcat/demo/index.jsp?rewrite=$1 [P,L,env=AJP_REDIRECT_REAL_URL:$1,QSA]
>         </Directory>
> </VirtualHost>
> 
> To illustrate the issue, I have set up a simple /demo/ application in Tomcat 10, but the problem is caused by the Apache2 webserver, so this part is not relevant here.
> 
> Before the upgrade, i.e. with apache <= 2.4.61-1~deb12u1, a request to http://127.0.0.1/foo/bar/?someparam will result in the following request being proxied to tomcat, as is expected:
>         GET /demo/index.jsp?rewrite=foo/bar/&someparam
> 
> After the upgrade to 2.4.62-1~deb12u1, the same requests gets mangled:
>         GET /demo/index.jsp%3Frewrite=foo/bar/&someparam?rewrite=foo/bar/&someparam
> 
> You can see that the complete parameter string is added twice now, with the leading ? being escaped the first time around, which in turn causes the path to be completely messed up, so Tomcat won't be able to find the file and returns a 404 status.
> 
> When turning on debug logging in apache2, one can see that the request path is still fine during mod_rewrite processing, it only gets broken during mod_proxy processing. The issue does not occur, when the RewriteRule is placed outside of the Directory block. Unfortunately, this is not a viable workaround for us, we really need to be able to use this inside <Directory> and we need the full flexibility of mod_rewrite too, so we cannot implement the same thing using ProxyPass, either. For now, the only resolution is to downgrade the apache2 packages:
> 
> apt -y --allow-downgrades install apache2=2.4.61-1~deb12u1 apache2-data=2.4.61-1~deb12u1 apache2-bin=2.4.61-1~deb12u1 apache2-utils=2.4.61-1~deb12u1
> 
> After the downgrade, the RewriteRule with the proxy directive is back to working as expected. As 2.4.62-1~deb12u1 contains security fixes, it feels like having to pin the previous apache2 version is not a good solution, but upgrading it is not possible until this is fixed.
> 
> If I had to guess, this may be caused by the following change:
> mod_proxy: Fix canonicalisation and FCGI env (PATH_INFO, SCRIPT_NAME) for
>      "balancer:" URLs set via SetHandler, also allowing for "unix:" sockets
>      with BalancerMember(s).  PR 69168.  [Yann Ylavic]

Can you double-check is this #1079172 and as reported upstream in
https://bz.apache.org/bugzilla/show_bug.cgi?id=69197 ? 

Regards,
Salvatore