Weakness · High
CWE-1223: Race Condition for Write-Once Attributes
What it is
A write-once register in hardware design is programmable by an untrusted software component earlier than the trusted software component, resulting in a race condition issue.
- Severity (our rating)
- High
- Likelihood of exploit
- Not rated by MITRE
- Introduced during
- Architecture and Design
- Exploited in the wild
- No CVE in CISA's catalog
In more detail
Integrated circuits and hardware IP software programmable controls and settings are commonly stored in register circuits. These register contents have to be initialized at hardware reset to defined default values that are hard coded in the hardware description language (HDL) code of the hardware unit. A common security protection method used to protect register settings from modification by software is to make them write-once. This means the hardware implementation only allows writing to such registers once, and they become read-only after having been written once by software. This is useful to allow initial boot software to configure systems settings to secure values while blocking runtime software from modifying such hardware settings. Implementation issues in hardware design of such controls can expose such registers to a race condition security flaw. For example, consider a hardware design that has two different software/firmware modules executing in parallel. One module is trusted (module A) and another is untrusted (module B). In this design it could be possible for Module B to send write cycles to the write-once register before Module A. Since the field is write-once the programmed value from Module A will be ignored and the pre-empted value programmed by Module B will be used by hardware.
What an attacker can do
- Bypass Protection Mechanism (Access Control)
How to prevent it
Architecture and Design
- During hardware design, all register write-once or sticky fields must be evaluated for proper configuration.
How to find it
- Automated Analysis. The testing phase should use automated tools to test that values are not reprogrammable and that write-once fields lock on writing zeros.
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Start freeSource: MITRE Common Weakness Enumeration, CWE version 4.19.1. CWE is a trademark of The MITRE Corporation.