Following the 4.4 release, you may have noticed a warning message when starting your teamserver:

The missing file is optional and its absence does not break the teamserver. It contains a number of optional parameters that can be used to customize the settings used to validate screenshot and keylog callback data, which allows you to tweak the fix for the “HotCobalt” vulnerability. You can suppress the warning by creating an empty file called TeamServer.prop and saving it in your Cobalt Strike directory.

An example TeamServer.prop file can be downloaded from the Cobalt-Strike/TeamServerProp GitHub repository here. We recommend that either an empty “TeamServer.prop” file is created, the file is created but the default settings are used, or the warning is simply ignored. If, however, you want to make changes to those settings, you’re now able to do so.

The default TeamServer.prop file contains the following:

#Cobalt Strike Team Server Properties
#Fri May 07 12:00:00 CDT 2021
# ------------------------------------------------
# Validation for screenshot messages from beacons
# ------------------------------------------------
# limits.screenshot_validated=true
# limits.screenshot_data_maxlen=4194304
# limits.screenshot_user_maxlen=1024
# limits.screenshot_title_maxlen=1024
# Stop writing screenshot data when Disk Usage reaches XX%
# Example: Off
#          "limits.screenshot_diskused_percent=0"
# Example: Stop writing screenshot data when Disk Usage reaches 95%
#          "limits.screenshot_diskused_percent=95"
# Default:
# limits.screenshot_diskused_percent=95
# ------------------------------------------------
# Validation for keystroke messages from beacons
# ------------------------------------------------
# limits.keystrokes_validated=true
# limits.keystrokes_data_maxlen=8192
# limits.keystrokes_user_maxlen=1024
# limits.keystrokes_title_maxlen=1024
# Stop writing keystroke data when Disk Usage reaches XX%
# Example: Off
#          "limits.keystrokes_diskused_percent=0"
# Example: Stop writing keystroke data when Disk Usage reaches 95%
#          "limits.keystrokes_diskused_percent=95"
# Default:
# limits.keystrokes_diskused_percent=95
  • Lines starting with “#” are comments.
  • limits.*_data_maxlen is the maximum size of screenshot/keylog data that will be processed. Callbacks exceeding this limit will be rejected.
  • limits.*_validated=false means that the three following “…_maxlen” settings are ignored
  • Setting any of the “…_maxlen” settings to zero will disable that particular setting
  • limits.*_diskused_percent sets the threshold for callback processing. Callbacks are rejected when disk usage exceeds the specified percentage
    • limits.*_diskused_percent=0 (zero) disables this setting
    • Valid values are 0-99