we are seeing a 403 - Forbidden not sure what happened......

Hi, Adding a 403 error image is not of much help. A bit more detail would usually be helpful.
If its designer you're trying to access, see if the user you log-in as has the designer privileges.

all users...all pages...it just started all of a sudden

Cloud or on-premise?

on-premise

Are you able to log-in using the default administrator account?
Are you using a SSL certificate? If so, is the certificate still valid?
If you're using SSO/silent authentication, check if there are any issue with the agent providing Appian with the valid header details
Is this dev or test or prod? If prod, please raise a support ticket with Appian support for assistance
For dev/test, were any recent changes or bulk modifications done to user identity? Did you configure LDAP settings etc., that the system is no longer able to use/reach?

no additional security was added...that I am aware of...
here is what is in the log

403_log.txt

Just a few suggestions to add to what Sathya has already said:

1. See if restarting the app server solves the problem
2. Review if the following file has been recently updated, if it has then restore it to the out of the box version
<APPIAN_HOME>\\ear\\suite.ear\\web.war\\WEB-INF\\conf\\security\\csrf\\whitelist-urlrewrite.xml
<APPIAN_HOME>\\runtime_ear\\suite.ear\\web.war\\WEB-INF\\conf\\security\\csrf\\whitelist-urlrewrite.xml
3. Review if there has been any updates to the files inside these directories

<APPIAN_HOME>\\ear\\suite.ear\\web.war\\WEB-INF\\conf\\security\\spring*.xml
<APPIAN_HOME>\\runtime_ear\\suite.ear\\web.war\\WEB-INF\\conf\\security\\spring*.xml

we did an upgrade to 7.7 effectively wiping out the appian directory and all seems right with the world...errors are no more...the upgrade took most of the day but it seems to have fixed our problem....thank you for the help