A flaw was found in SSSD (System Security Services Daemon). A local attacker with privileges to connect to the PAM (Pluggable Authentication Modules) responder socket can send a specially crafted protocol request. If the pam_app_services configuration is enabled and the service item is omitted from the request, a NULL pointer dereference can occur. This vulnerability leads to a denial of service, causing the PAM responder to crash and disrupt authentication services.
To mitigate this issue, avoid configuring pam_app_services in the [pam] section of /etc/sssd/sssd.conf if it is not operationally required. If pam_app_services is configured, remove or comment out the pam_app_services line and restart the sssd service.
Example:
```
<h1>/etc/sssd/sssd.conf</h1>
[pam]
<h1>pam_app_services = app_svc</h1>
```
After modifying the configuration, restart the SSSD service:
systemctl restart sssd
Note that restarting the SSSD service may temporarily interrupt authentication and authorization services.