| There are two types of IDPS updates: software updates and signature updates. Software updates fix bugs in the IDPS software or add new functionality, while signature updates add new detection capabilities or refine existing detection capabilities (e.g., reducing false positives). For many IDPSs, signature updates cause program code to be altered or replaced, so they are really a specialized form of software update. For other IDPSs, signatures are not written in code, so a signature update is a change to the configuration data for the IDPS.
Software updates can include any or all IDPS components, including sensors, agents, management servers, and consoles. Software updates for sensors and management servers, particularly appliance-based devices, are often applied by replacing an existing IDPS CD with a new one and rebooting the device. Many IDPSs run the software directly from the CD, so that no software installation is required. Other components, such as agents, require an administrator to install software or apply patches, either manually on each host or automatically through IDPS management software. Some vendors make software and signature updates available for download from their Web sites or other servers; often, the administrator interfaces for IDPSs have features for downloading and installing such updates.
Administrators should verify the integrity of updates before applying them, because updates could have been inadvertently or intentionally altered or replaced. The recommended verification method depends on the update’s format, as follows:
Files downloaded from a Web site or FTP site. Administrators should compare file checksums provided by the vendor with checksums that they compute for the downloaded files.
Update downloaded automatically through the IDPS user interface. If an update is downloaded as a single file or a set of files, either checksums provided by the vendor should be compared to checksums generated by the administrator, or the IDPS user interface itself should perform some sort of integrity check. In some cases, updates might be downloaded and installed as one action, precluding checksum verification; the IDPS user interface should check each update’s integrity as part of this.
Removable media (e.g., CD, DVD). Vendors may not provide a specific method for customers to verify the legitimacy of removable media apparently sent by the vendors. If media verification is a concern, administrators should contact their vendors to determine how the media can be verified, such as comparing vendor-provided checksums to checksums computed for files on the media, or verifying digital signatures on the media’s contents to ensure they are valid. Administrators should also consider scanning the media for malware, with the caveat that false positives might be triggered by IDPS signatures for malware on the media.