Limiting File Size Upload using Custom Signature

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Limiting File Size Upload using Custom Signature

L1 Bithead

Users in enterprise often use web based file hosting to upload big files. This creates concerns in the usage of networks bandwidth and server storage capacity, as the file can be bigger than 1GB. Below steps are usefull to control file size uploaded to a web server using HTTP Request Content-Length parameter.


PAN-OS version: 6.1.0-b43



  1. Create a custom signature vulnerability


Go to Objects Tab > Custom Objects > Vulnerability, then click “Add”,

Fill-in required fields as shown below:


Click “Signatures” Tab, then click “Add”. In Standard window, type in the Signature Name:



At the bottom of “Standard” window, click “Add And Condition”:



Inside “Or Condition” window, choose Operator to “Greater Than”, choose Context to “http-req-content-length”. To limit file size up to 10 MB, we need to fill-in the Value in bytes, 10MB equals to “10485760”



Then click “OK”, click “OK” again.


Or, you can just save below text as BLOCK-FILE-10MB.xml file and click “Import” in Objects Tab > Custom Objects > Vulnerability.


<vulnerability-threat version="6.1.0">

<entry name="41001">



       <entry name="BLOCK-FILE-10MB">


           <entry name="And Condition 1">


               <entry name="Or Condition 1">























  1. Create a Vulnerability Protection profile


Go to Objects Tab > Security Profiles > Vulnerability Protection, then click “Add”,

You can name the profile as “VP-FILE-UPLOAD”:


Then click “Add”, and fill-in Rule Name, Theat Name, and others similarly as below picture:



After finish, then click “OK”, click “OK”.


  1. Create Security Policy


Go to Policies Tab > Security, then create security policy similarly as below:




Don’t forget to assign vulnerability protection profile “VP-FILE-UPLOAD” under “Actions” tab:



Click “OK”, then click “Commit”.


  1. File Upload Testing


Open the browser, and type

Click “Choose File”, then find any file larger than 10MB:


When uploading a file with size more than 10MB (10485760 bytes), the firewall block and reset the connection.


Below is the capture of the packet that show “Content-Length” value is more than 10MB:


And the browser shows blank page:




  1. Check Firewall Threat Logs


Threat Logs shows the firewall catch “Content-Length” parameter which is greater than allowable size.




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