Indicators of Behavior (IOBs) in SPARTA v3.0

By leveraging IOBs, space mission operators can detect subtle deviations that may indicate malicious intent​.

Authors: Brandon Bailey, Brad Roeher, Randi Tinney and Ernest Wong

One of the most innovative additions to SPARTA v3.0 is the creation of IOBs specifically tailored to onboard spacecraft activity. The creation of IOBs in SPARTA v3.0 was funded by the Department of Homeland Security (DHS) Science and Technology (S&T) Directorate to enhance the cybersecurity posture of space systems, addressing the growing need for proactive threat detection as space infrastructure becomes increasingly critical to national security and economic stability. Unlike traditional Indicators of Compromise (IOCs), which focus on detecting known malicious artifacts or signatures, IOBs are designed to identify behavioral patterns that could indicate emerging threats. This proactive approach allows space system developers to build detection mechanisms for anomalies and suspicious activities onboard the spacecraft, making IOBs a crucial element in modern spacecraft defense​.

Why IOBs Matter for Space Cybersecurity

Spacecraft are typically designed to be highly specialized and deterministic, where deviations from expected behavior often indicate either a system fault or potential adversarial activity. IOBs bridge this gap by focusing on behavioral anomalies in addition to known signatures, making them particularly effective in environments with limited historical data on cyber incidents. This is essential for space missions where threats may emerge without warning or established patterns. By leveraging IOBs, space mission operators can detect subtle deviations, such as unexpected command execution rates, unusual memory utilization, or anomalous network traffic, that may indicate malicious intent​.

How to Build IOBs for Space Cybersecurity

Building IOBs for space systems involves a structured process that translates threat-based information into practical and observable behaviors that can be used for detection and response. To begin deriving IOBs, we leveraged SPARTA as a source of realistic attack vectors and to serve as the foundation for understanding what behaviors matter and how they may manifest operationally onboard a spacecraft.

Given the large number of techniques in SPARTA, prioritization was essential for establishing the initial IOB baseline. To support this, we used SPARTA’s Notional Risk Scores (NRS) which is a risk assessment model designed to help engineers focus on the most critical threats. NRS assigns a risk value to each technique based on the potential impact to the system and the likelihood that an adversary within a given threat tier could successfully execute it. These scores are informed by previous work detailed in Aerospace Report TOR-2021–01333-REV A, which introduced a high-level threat model and categorized adversary capabilities into threat tiers. This provides a structured way to estimate risk in environments where attack likelihood is difficult to assess due to the uniqueness of each mission.

By focusing on techniques with high NRS scores, we ensured that the first release of IOBs targets high-impact, plausible threat scenarios. Each selected technique was analyzed to understand what behavioral evidence might indicate its use. This methodical, threat-driven approach provides a scalable foundation for IOB development. Once developed, these IOBs were systematically mapped to specific SPARTA techniques which not only ensures consistency across threat detection efforts but also allows users to see how behavioral indicators directly relate to adversarial tactics. By linking IOBs to techniques, cybersecurity practitioners can implement them in their monitoring frameworks with a clear understanding of the associated risks and attack vectors.

As additional space missions are assessed and more telemetry, signal, and operational anomalies are observed, the IOB set can evolve to ensure space systems remain resilient against both known and emerging adversary behaviors. Continued growth and refinement of these indicators will depend heavily on community engagement, which is why contributions through the Space Information Sharing and Analysis Center (S-ISAC) are critical. By collaborating through S-ISAC, we can crowdsource insights, share real-world threat data, and avoid duplicative efforts. This will ensure the broader space community benefits from a unified and constantly improving understanding of space-based threats.

Building Intrusion Detection Systems with IOBs

One of the key applications for IOBs is in building and enhancing Intrusion Detection Systems (IDSs) for spacecraft. Some IDSs solutions rely only on signature-based detection via IOCs, which may not suffice in a rapidly evolving threat landscape. With IOBs, IDS can be properly tuned to detect behavioral anomalies, such as unauthorized command execution during safe-mode or unexpected memory modifications. By integrating these IOBs into onboard IDSs, spacecraft operators gain the ability to detect not just known threats but also emerging patterns that could indicate compromise. This level of detection is critical for maintaining mission assurance in the face of sophisticated cyber adversaries​.

Integrating IOBs directly into spacecraft, we can address emerging cyber threats and ensure continuous protection, even when communication with ground stations is delayed or interrupted. The development of onboard intrusion detection will become a critical piece in space system defense strategies, helping protect against malicious activities, system manipulation, or protocol-based attacks that can compromise spacecraft operations. Given how quickly an attack can manifest onboard, ground operators may not have time to intervene before they lose control of the spacecraft. In this evolving threat landscape, the move towards on-orbit, autonomous cyber defense capabilities is essential to safeguard future space missions. Having documented IOBs will greatly enhance the detection, correlation, and response capabilities of these platforms by monitoring for specific malicious or anomalous behaviors in spacecraft operations.

To effectively leverage IOBs in intrusion detection, we chose to document them using the Structured Threat Information Expression (STIX) format. STIX is particularly well-suited for capturing behavioral indicators because its flexible and expressive structure allows for detailed representation of complex threat patterns. By using STIX, we provide a standardized way to define IOBs that can be directly integrated into IDS implementations. This approach not only enhances consistency but also supports the creation of detection logic. Feedback from the community has highlighted that the STIX format, with its Boolean and pattern-matching capabilities, greatly facilitates building automated detection rules, helping spacecraft software developers quickly build detections for indicators.

In order for these IOBs to be effective in detecting threats or anomalies in spacecraft operations, it is essential that the necessary data is available for analysis. Without access to critical telemetry, network traffic logs, process activity, and other system data, even the most sophisticated detection logic will be rendered useless. The spacecraft must ensure that this data is collected, transmitted, and stored in a reliable manner so that it can be analyzed in realtime. This includes having robust logging mechanisms in place to capture communication protocols, system resource usage, file integrity, and command execution events. Data availability is the foundation of any detection and response strategy and without it, the visibility needed to identify threats is impaired, leaving the spacecraft vulnerable to undetected attacks.

Organizing IOBs: Behavioral Categories

IOBs are currently organized within SPARTA into 10 distinct categories, where each IOB has their own unique identifiers. More categories could be added later as more indicators are researched, but these 10 categories will structure the new SPARTA v3.0 IOB interface:

1. Unauthorized and Anomalous Command Execution (UACE)

UACE IOBs focus on detecting unauthorized, anomalous, or malicious command executions targeting spacecraft operations. It includes monitoring commands issued outside expected time windows, deviations from baseline configurations, and replay attacks. UACE also covers unauthorized actions during safe-mode, where reduced security measures can be exploited. These IOBs help spacecraft operators identify and respond to command-related anomalies that may jeopardize mission integrity​.

2. Unauthorized Cryptographic Key Usage and Encryption Bypass (UCEB)

UCEB IOBs target unauthorized access, misuse, or tampering with cryptographic keys and encryption mechanisms. Monitoring includes repeated cryptographic key usage from unexpected locations, improper access to decryption keys, and any unexpected changes to encryption configurations. UCEB IOBs are critical for detecting persistent access attempts or data exfiltration efforts that exploit weakened encryption practices​.

3. Communication Security and Network Exploitation (CSNE)

CSNE IOBs detect unauthorized access and exploitation targeting spacecraft communication channels. They include monitoring network traffic from rogue ground stations, unexpected protocols, or IP addresses, as well as bandwidth spikes or communication link anomalies that might indicate jamming or network exploitation. By focusing on communication integrity, CSNE IOBs help detect potential command injection and data interception threats.

4. Authentication and RF Signal Integrity Threats (ARFS)

ARFS IOBs focus on threats to authentication mechanisms and RF communication integrity. This includes monitoring for abnormal authentication attempts, RF signal manipulation, and replay attacks. This category is vital for identifying electronic warfare tactics designed to compromise spacecraft control through signal jamming or spoofing​.

5. GNSS and Time Manipulation Threats (GNTM)

GNTM IOBs focus on GNSS and timing data, which are critical for spacecraft navigation and synchronization. This category includes IOBs for detecting GNSS interference, time spoofing, and irregularities in time synchronization that may indicate manipulation. Monitoring for GNSS signal delays, signal-to-noise ratio drops, or unauthorized time adjustments helps maintain mission accuracy and stability.

6. Spacecraft Memory Integrity and Resource Exploitation Attacks (MIRE)

MIRE IOBs focus on unauthorized memory access or modification, including attacks on flash memory, EEPROM, and boot processes. They also cover resource exploitation tactics, such as memory exhaustion or the insertion of malicious code into boot memory. Detecting these threats helps protect critical system functions from disruption and unauthorized control​.

7. Watchdogs and Register Exploitation (WTRE)

WTRE IOBs address threats to watchdog timers and critical subsystem registers. IOBs include detecting unauthorized access or manipulation of watchdog functions that may disrupt spacecraft stability. Monitoring for changes to critical registers or timing inconsistencies helps identify potential sabotage or subsystem compromise​.

8. Software Integrity and Unauthorized Updates (SIUU)

SIUU IOBs detect the manipulation or unauthorized modification of flight software, including malicious updates or firmware tampering. Monitoring includes checking software integrity, update validation, and unauthorized software modifications. This category helps ensure that software configurations remain secure throughout the spacecraft’s operational life​.

9. Spacecraft Sensor Manipulation and System Resource Exploitation (SMSR)

SMSR IOBs address threats to spacecraft sensors, which are critical for attitude control and system monitoring. SMSR IOBs detect manipulation of sensor data or attempts to exploit system resources. Examples include false telemetry injection or sensor spoofing that may mislead spacecraft operations. Early detection helps maintain accurate control and prevents resource depletion​.

10. Data Integrity and Storage Exploitation Threats (DISE)

DISE IOBs focus on maintaining data integrity and protecting onboard storage from unauthorized modification or data corruption. DISE IOBs monitor file system integrity, data manipulation attempts, and unauthorized data deletions. By securing critical data, spacecraft operators can protect mission continuity and prevent data loss​.

The introduction of IOBs in SPARTA v3.0 marks the first-ever comprehensive documentation of potential malicious behavior specifically targeting spacecraft. As the first release and baseline for space system IOBs, this represents a foundational step in advancing space cybersecurity. We recognize that as research progresses and more information becomes available, future releases will expand and refine these IOBs, providing even greater coverage and precision. This ongoing effort reflects our commitment to enhancing threat detection and response in the evolving space threat landscape. Stay tuned for updates as we continue to develop and publish new IOBs to meet emerging challenges.