Issue Summary

This is reproducible on Data Center: (yes)

This is a continuation of the bug CONFSERVER-93655 - Getting HTTP 400 while saving page by using the close button..

If the page template contains one of the following character sets in the content the saving process gets a HTTP 400 message.

../ 
..\ 
…/ 
…\

Steps to Reproduce

1. Create a fresh instance with Confluence 8.5.5
2. Create a new page template by navigating to General Configuration —> Global Templates and Blueprints
3. Insert ../ to the template and save it
4. Gets HTTP 400

The same issue can be reproduce if we try to add the code in Stylesheet as well. This actually works correctly, we don't want to let path traversal strings in stylesheets.

1. Choose Administration   > General Configuration > Stylesheet. 
2. Choose Edit.
3. Insert ../ to the template and save it
4. Gets HTTP 400

Expected Results

The saving process should be completed properly.

Actual Results

Getting HTTP 400 message after clicking the save button.

Workaround

Replace the below character sets with ./ or .\ to resolve the save process.

../ 
..\ 
…/ 
…\