On July 2, 2013 Rapid 7 published a guide to security penetration testing of the latest IPMI 2.0 protocol and implementations by various vendors.
Vendors have provided patches that remediate most of the vulnerabilities, but the “IPMI 2.0 RAKP Authentication Remote Password Hash Retrieval” vulnerability has not yet been addressed. This arises from the difficulty that the IPMI 2.0 specification is flawed in that it reveals the password hash and salt to anonymous remote clients. This allows for offline brute force attacks. Complete remediation will require a change to the IPMI specification.
An IPMI sub-system consists of a main controller, called the baseboard management controller (BMC) and other management controllers distributed among different system modules that are referred to as satellite controllers. The satellite controllers within the same chassis connect to the BMC via the system interface called Intelligent Platform Management Bus/Bridge (IPMB) — an enhanced implementation of I²C (Inter-Integrated Circuit). The BMC connects to satellite controllers or another BMC in another chassis via the Intelligent Platform Management Controller (IPMC) bus or bridge. It may be managed with the Remote Management Control Protocol (RMCP), a specialized wire protocol defined by this specification. RMCP+ (a UDP-based protocol with stronger authentication than RMCP) is used for IPMI over LAN.
Interfaces to the baseboard management controller
Several vendors develop and market BMC chips. A BMC utilized for embedded applications may have limited memory and require optimized firmware code for implementation of the full IPMI functionality. Highly integrated BMCs can provide complex instructions and provide the complete out-of-band functionality of a service processor. The firmware implementing the IPMI interfaces is provided by various vendors. A field replaceable unit (FRU) holds the inventory, such as vendor ID and manufacturer, of potentially replaceable devices. A sensor data record (SDR) repository provides the properties of the individual sensors present on the board. For example, the board may contain sensors for temperature, fan speed, and voltage.
Baseboard management controller
The baseboard management controller (BMC) is the intelligence in the IPMI architecture. It is a specialized microcontroller embedded on the motherboardof a computer, generally a server. The BMC manages the interface between system management software and platform hardware.
Different types of sensors built into the computer system report to the BMC on parameters such astemperature, cooling fan speeds, power status,operating system (OS) status, etc. The BMC monitors the sensors and can send alerts to a system administratorvia the network if any of the parameters do not stay within preset limits, indicating a potential failure of the system. The administrator can also remotely communicate with the BMC to take some corrective action such as resetting or power cycling the system to get a hung OS running again. These abilities save on the total cost of ownership of a system.
Physical interfaces to the BMC include SMBus buses, an RS-232 serial console, address and data lines and an Intelligent Platform Management Bus (IPMB), that enables the BMC to accept IPMI request messages from other management controllers in the system.
A direct serial connection to the BMC is not encrypted as the connection itself is secure. Connection to the BMC over LAN may or may not use encryption depending on the security concerns of the user.
There are rising concerns about the general security regarding BMCs as a closed infrastructure.
As well as using a separate dedicated management LAN connection, IPMI also allows implementation of what is often called a “side-band” management LAN connection. This connection utilizes a System Management Bus (SMBUS) interface between the BMC (Baseboard Management Controller) and the board Network Interface Controller (NIC). This solution has the advantage of reduced costs but also provides limited bandwidth – sufficient for text console redirection but not for video redirection. For example, when a remote computer is down the system administrator can access it through IPMI and utilize a text console. This will be sufficient for a few vital functions, such as checking the event log, accessing the BIOS setup and perform power on, power off or power cycle. However, more advanced functions, such as remote re-installation of an operating system, may require a full out-of-band management approach utilizing a dedicated LAN Connection.
As a message-based, hardware-level interface specification, IPMI operates independently of the operating system (OS) to allow administrators to manage a system remotely in the absence of an operating system or of the system management software. Thus IPMI functions can work in any of three scenarios:
- before an OS has booted (allowing – for example – the remote monitoring or changing of BIOS settings)
- when the system is powered down
- after OS or system failure – the key characteristic of IPMI compared with in-band system management such as by remote login using SSH
Using a standardized interface and protocol allows systems-management software based on IPMI to manage multiple disparate servers.
System administrators can use IPMI messaging to monitor platform status (such as system temperatures, voltages, fans, power supplies and chassis intrusion); to query inventory information; to review hardware logs of out-of-range conditions; or to perform recovery procedures such as issuing requests from a remote console through the same connections e.g. system power-down and rebooting, or configuring watchdog timers. The standard also defines an alerting mechanism for the system to send a simple network management protocol (SNMP) platform event trap (PET).
The monitored system may be powered off, but must be connected to a power source and to the monitoring medium, typically a local area network (LAN) connection. IPMI can also function after the operating system has started, and exposes management data and structures to the system management software. IPMI prescribes only the structure and format of the interfaces as a standard, while detailed implementations may vary. An implementation of IPMI version 1.5 can communicate via a direct out-of-band local area network (LAN) or serial connection or via a side-band local area network (LAN) connection to a remote client. The side-band LAN connection utilizes the board network interface controller (NIC). This solution is less expensive than a dedicated LAN connection but also has limited bandwidth. Systems compliant with IPMI version 2.0 can also communicate via serial over LAN, whereby serial console output can be remotely viewed over the LAN. Systems implementing IPMI 2.0 typically also include KVM over IP, remote virtual media and out-of-band embedded web-server interface functionality, although strictly speaking, these lie outside of the scope of the IPMI interface standard.
DCMI (Data Center Management Interface) is a similar standard based on IPMI but designed to be more suitable for Data Center management: it uses the interfaces defined in IPMI, but minimizes the number of optional interfaces and includes power capping control, among other differences.