FortiWeb - Cookie signed verification failed

[romank]

Hello,

I have a few services exposed over FortiWeb, many profiles enabled including "Cookie Security Policy"

im struggling witj error below that is blocking trafic if"alert_and_deny" im not sure why there is "signed verification failed". How to troubleshoot it?

Cookie name (AMP_899c7e29a9), signed verification failed; track lost; Domain: some.domain..com; Path: /somepath/

[spoojary]

The error you're seeing from FortiWeb's "Cookie Security Policy" suggests a possible integrity issue with the AMP_899c7e29a9 cookie. To troubleshoot:

1. Review the Policy: Familiarize yourself with FortiWeb's "Cookie Security Policy" settings to understand its cookie verifications.
2. Check Logs: Examine FortiWeb logs for deeper insights on the error. Look for patterns like specific sources or times.
3. Origin & Integrity: Determine which service sets this cookie. Ensure it's generated and signed correctly per FortiWeb's standards.
4. Client-Side Checks: Use a clean browser environment to check if browser extensions or scripts are affecting the cookie.
5. Adjust Policy: Based on your findings, either modify the service setting the cookie or fine-tune the FortiWeb policy.
6. Documentation & Support: Refer to FortiWeb's official documentation for more insights, and if unresolved, contact Fortinet's technical support.

[romank]

Of course i did check logs and seen which particular cookie is problematic, but i dont understand why is it.. I guess i'll need to get deeply into this - how forti is processing it. There must be sth that couses such errors. I suspecting at first " track lost".

Its weird for me that forti couldn't check such cookie, so it will not prevent poisoning.

[anignan]

Hi @romank 

It is happening for all users? Seems like a device is changing the cookie which is not matching the one that is being cache by FortiWeb for the session.

Abdel

NSE4,5x2,6x2,7x4

[romank]

Yes, its happening for all users, I was also thinking that maybe there is some expiration date on destination server? i did enable expiration of cookie for 15min  - just for testing but no special result i got :)

[shafiq23]

Hello romank,

As per FortiWeb Administration Guide on Cookie Security "Signed" mode, FortiWeb will track cookies value responded by web server in the first HTTP/S request from the client, hash it and track if there is any tampering in the following requests.

https://docs.fortinet.com/document/fortiweb/7.2.4/administration-guide/2851/cookie-security

The cookie name mentioned (AMP_899c7e29a9) value may have changed and FortiWeb took action according to configured action in the cookie security policy. Please refer below for possible solutions;

1. Change to "Encrypted" mode - works in some cases where cookies value keeps on changing(not preferred if you would like to prevent cookie poisoning attack)
2. Do exceptions according to the cookie name

Thanks.

Regards,

Shafiq