Mar 27, 2026 - For details about updated CVE-2025-53521 (BIG-IP APM vulnerability), refer to K000156741.

Forum Discussion

Antonio3's avatar
Antonio3
Icon for Altocumulus rankAltocumulus
Mar 27, 2026

block a specific user

Hi everyone,

Is it possible to create a signature to block a specific user from authenticating to a web portal?

 

thanks

 

 

Antonio

4 Replies

  • Jmtaylor's avatar
    Jmtaylor
    Icon for Moderator rankModerator
    Mar 27, 2026

    Antonio3​ 
    Yes, this is possible using BIG-IP ASM/Advanced WAF custom attack signatures. The approach is to match the specific username value submitted in the login request (e.g., in a POST body parameter, cookie, or header) and block it.
     Let us know if you need more information 

  • Antonio3's avatar
    Antonio3
    Icon for Altocumulus rankAltocumulus
    Mar 30, 2026

    Thanks for your reply.

    I created a new signature as shown in the attached image.

    This happens: it blocks all authentication requests containing the word admin, for example:

     

    user:admin

    password:admin

     

    user:administrator

    password:pippo

     

    user:pippo

    password:admin

     

    user:adminarial

    password:pippo

     

    I'd like it to block only when the "admin" username is entered.

     

    Thanks

     

    • waseem-alomari's avatar
      waseem-alomari
      Icon for Nimbostratus rankNimbostratus
      Mar 31, 2026

      I guess that you need to change the  ( Matched Criteria ) from contains string to something more accurate from the available options , or to match on regular expressions which will give only " admin "