Issue Problem with web application firewall - file extension is restricted by policy

[Ras Alghul]

Server operating system version

Plesk Obsidian v18.0.58_build1800240123.15 os_Ubuntu 22.04

Plesk version and microupdate number

Plesk Obsidian v18.0.58_build1800240123.15 os_Ubuntu 22.04

Hi,

We are experiencing an issue with one of our customers, unique to their case.

They encounter difficulties accessing our Nextcloud installation when the Web Application Firewall is enabled. This user, who operates on both Mac and iPhone, faces constant rejections. This issue persists whether they use the Nextcloud app or the desktop application, and even attempts to connect via an HTTPS browser result in rejection.

Upon reviewing the log files, this problem's cause remains unclear. It's particularly puzzling as other Apple Mac users do not encounter these issues.

Could you help us understand why this is happening and why it's isolated to this specific user?

--f7d4e022-H--
Message: Access denied with code 403 (phase 2). Match of "pmFromFile userdata_wl_extensions" against "TX:extension" required. [file "/etc/apache2/modsecurity.d/rules/comodo_free/10_HTTP_HTTP.conf"] [line "27"] [id "210730"] [rev "5"] [msg "COMODO WAF: URL file extension is restricted by policy||customer.domain.com|F|2"] [data ".com"] [severity "CRITICAL"] [tag "CWAF"] [tag "HTTP"]
Apache-Error: [file "apache2_util.c"] [line 275] [level 3] [client 80.187.80.166] ModSecurity: Access denied with code 403 (phase 2). Match of "pmFromFile userdata_wl_extensions" against "TX:extension" required. [file "/etc/apache2/modsecurity.d/rules/comodo_free/10_HTTP_HTTP.conf"] [line "27"] [id "210730"] [rev "5"] [msg "COMODO WAF: URL file extension is restricted by policy||customer.domain.com|F|2"] [data ".com"] [severity "CRITICAL"] [tag "CWAF"] [tag "HTTP"] [hostname "customer.domain.com"] [uri "/remote.php/dav/files/user@domain.com"] [unique_id "ZcCchXhdkYMpOqMcyyQ3eQAAAI4"]
Action: Intercepted (phase 2)
Apache-Handler: proxy:unix:/var/www/vhosts/system/customer.domain.com/php-fpm.sock|fcgi://127.0.0.1:9000
Stopwatch: 1707121797791133 788374 (- - -)
Stopwatch2: 1707121797791133 788374; combined=1391, p1=556, p2=705, p3=0, p4=0, p5=129, sr=142, sw=1, l=0, gc=0
Producer: ModSecurity for Apache/2.9.7 (http://www.modsecurity.org/); CWAF_Apache.
Server: Apache
Engine-Mode: "ENABLED"

I'm struggling to understand the issue related to the file extension.

Interestingly, when the Application Firewall is disabled, this particular user does not experience any problems. This further complicates our understanding of the issue.

 

[Peter Debik]

The request offends rule no. 210730. You can add rule no. 210730 to the lists of exceptions in the "Web Application Firewall" icon of the domain. Store the new configuration, then try again.

 

[Ras Alghul]

Wow thank you very much, I added the exception and now I wait for my customer what experience he has after this.
I researched that rule but even with Chatgpt4 I didn't understand it well. But lets not go too deep in the rabbithole

 

[Linulex]

uri "/remote.php/dav/files/user@domain.com

This is the problem. WAF thinks you are trying to access a file with a .com extension.

.com is an old executable extension, but they are still used, on windows 10 in c:\windows\system32 there are still a few .com files. format.com, tree.com, chcp.com, etc...

COM - DOS Command File Format

Learn about COM file format and APIs that can create and open COM files.

docs.fileformat.com

regards
Jan