Varnish caching POST requests from Server Side Security scanner

Question

I run a webstore on Magento ver. 2.1.8 eCommerce platform.

Recently, I came across a issue where front-end of my website was using a completely different colour skin and layout and couldn't figure out why this is happening.

Purging the Varnish cache solved the issue for some time as the website would randomly changed the skin again after some time. I had no idea how Varnish was caching the content that should never be displayed.

I also use Acunetix as a Server Side Scanner which scans my website every week for any malicious code or gaps in security. I found one of the POST request that it sent:

POST /themesettings/index/paneltool/ HTTP/1.1
Content-Length: 1193
Content-Type: multipart/form-data; boundary=-----Boundary_JTWCAHJSKP
Referer: https://www.domain.co.uk/
Cookie: PHPSESSID=sadfq345r234324dfasd; mage-messages= vespaneltool=a%3A6%3A%7Bs%3A52%3A%22ves_themesettings_general%2Fgeneral_settings%2Fdirection%22%3Bs%3A3%3A%22rtl%22%3Bs%3A49%3A%22ves_themesettings_general%2Fgeneral_settings%2Flayout%22%3Bs%3A8%3A%22boxed-lg%22%3Bs%3A52%3A%22ves_themesettings_general%2Fgeneral_settings%2Fmax_width%22%3Bs%3A5%3A%22960px%22%3Bs%3A59%3A%22ves_themesettings_general%2Fgeneral_settings%2Fmax_width_custom%22%3Bs%3A8%3A%22gqwtkdks%22%3Bs%3A47%3A%22ves_themesettings_general%2Fgeneral_settings%2Fskin%22%3Bs%3A8%3A%22blue.css%22%3Bs%3A55%3A%22ves_themesettings_header%2Fgeneral_settings%2Fheader_layout%22%3Bs%3A13%3A%22default.phtml%22%3B%7D; _vwo_uuid_v2=EC7CC959823F97596222AB508A6BB8BE|53a815cb661ea346311131469aaeb1c2; PHPSESSID=oaibesqi4980brc3udl1gdrfb0
Host: www.domain.co.uk
Connection: Keep-alive
Accept-Encoding: gzip,deflate
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.21 (KHTML, like Gecko) Chrome/41.0.2228.0 Safari/537.21
Accept: */*

-------Boundary_JTWCAHJSKP
Content-Disposition: form-data; name="btn-save"

Apply
-------Boundary_JTWCAHJSKP
Content-Disposition: form-data; name="userparams[ves_themesettings_general/general_settings/direction]"

rtl
-------Boundary_JTWCAHJSKP
Content-Disposition: form-data; name="userparams[ves_themesettings_general/general_settings/layout]"

boxed-md
-------Boundary_JTWCAHJSKP
Content-Disposition: form-data; name="userparams[ves_themesettings_general/general_settings/max_width]"

1024px
-------Boundary_JTWCAHJSKP
Content-Disposition: form-data; name="userparams[ves_themesettings_general/general_settings/max_width_custom]"

12345'"\'\");|]*%00{%0d%0a<%00>%bf%27'ð©
-------Boundary_JTWCAHJSKP
Content-Disposition: form-data; name="userparams[ves_themesettings_general/general_settings/skin]"

aquamarine.css
-------Boundary_JTWCAHJSKP
Content-Disposition: form-data; name="userparams[ves_themesettings_header/general_settings/header_layout]"

default2.phtml
-------Boundary_JTWCAHJSKP
Content-Disposition: form-data; name="vespanel"

1
-------Boundary_JTWCAHJSKP
Content-Disposition: form-data; name="vesreset"

0
-------Boundary_JTWCAHJSKP--

The above is the configuration of the wrong designed that was cached by Varnish. Eg aquamarine.css is the wrong CSS file cached, it should be red.css .

Is it possible that after this post request, Varnish cached this settings? Also, what is the best way to overcome this problem? Should I create a rule in Acunetix to avoid this URL? Or create a NginX configuration to block access to it?

Answer 1

Try something like the following to just force Varnish to not attempt to use (or store into) the cache for POST requests:

sub vcl_recv {
    if (req.method == 'POST') {
       set req.hash_always_miss = true;
    }
}