9.1 - VU#163057

Overview

The Intelligent Platform Management Interface (IPMI) implementations in multiple manufacturer's Baseboard Management Controller (BMC) software are vulnerable to IPMI session hijacking. An attacker with access to the BMC network (with IPMI enabled) can abuse the lack of session integrity to hijack sessions and execute arbitrary IPMI commands on the BMC.

Description

IPMI is a computer interface specification that provides a low-level management capability independent of hardware, firmware, or operating system. IPMI is supported by many BMC manufacturers to allow for transparent access to hardware. IPMI also supports pre-boot capabilities of a computer such as selection of boot media and boot environment. BMCs are recommended to be accessible via dedicated internal networks to avoid risk of exposure.

IPMI sessions between a client and a BMC follow the RAKP key exchange protocol, as specified in the IPMI 2.0 specification. This involves a session ID and a BMC random number to uniquely identify an IPMI session. The security researcher, who wishes to remain anonymous, has attempted to disclose two vulnerabilities related to BMC software and session management. The first vulnerability identifies the use of weak randomization while interacting with a BMC using IPMI sessions. The researcher discovered that if both the IPMI session ID and BMC's random number are predictable or constant, an attacker can either hijack a session or replay a session without knowing the password that was set to protect the BMC. The second vulnerability from the reporter identifies certain cases where the BMC software fails to enforce previously negotiated IPMI 2.0 session parameters, allowing an attacker to either downgrade or disable session verification. Due to the reuse of software or libraries, these vulnerabilities may be present in multiple models of BMC. It is recommended that sufficient precaution is taken in protecting datacenters and cloud installations with multiple servers to protect IPMI session interaction using both the software updates and the recommendations to secure and isolate the networks where IPMI is accessible.

Impact

An unauthenticated attacker with access to the BMC network can predict IPMI session IDs and/or BMC random numbers to replay a previous session or hijack an IPMI session. This can allow the attacker to inject arbitrary commands into the BMC and be able to perform high-privileged functions (reboot, power-off, re-image of the machine) that are available to the BMC.

Solution

Apply an update

Please consult the Vendor Information section for information provided by BMC vendors to address these vulnerabilities.

Restrict access

As a general good security practice, only allow connections from trusted hosts and networks to the BMC network that exposes the IPMI enabled interface.

Acknowledgements

Thanks to the security researcher who would like to remain anonymous for researching and reporting these vulnerabilities.

This document was written by Ben Koo.