CVE-2026-77234

Executive Summary

CVE-2026-77234 is an improper input validation flaw in FreeRTOS-Kernel versions prior to 11.3.1, affecting MPU-enabled ports. An unprivileged task can leverage this flaw to execute arbitrary code in privileged kernel context, resulting in full system compromise. The vulnerability carries a CVSS score of 8.8 (High) with a scope change indicating that the impact extends beyond the initially compromised component. No public exploit code exists at the time of writing, but the attack surface — embedded systems running FreeRTOS with Memory Protection Unit (MPU) enabled — includes a wide range of IoT devices, and the privilege escalation potential warrants immediate remediation.

Technical Analysis

FreeRTOS is a widely deployed real-time operating system (RTOS) for embedded and IoT devices. The "FreeRTOS-Kernel" designation refers to the core kernel component that manages tasks, scheduling, inter-process communication, and memory handling.

The vulnerability class is Improper Input Validation (CWE-863, also aligned with the CWE-863 "Incorrect Authorization" related classification). The specific flaw resides in the kernel's handling of inputs from unprivileged tasks when the Memory Protection Unit (MPU) is enabled. The MPU is a hardware feature that enforces privilege boundaries between tasks, and FreeRTOS provides MPU support on select architectures (e.g., ARM Cortex-M variants).

The NVD description states that "improper input validation in FreeRTOS-Kernel before 11.3.1 might allow an unprivileged task on MPU-enabled ports to execute code in privileged kernel context." This indicates that the kernel fails to sufficiently validate certain inputs passed by a task before acting on them in kernel mode (e.g., during system calls or privilege-transitioning operations). Because the input flows from the unprivileged task into the kernel's privileged execution path, an attacker who can control or influence that input can manipulate kernel behavior — potentially redirecting execution flow, modifying kernel data structures, or altering memory access permissions.

The precise code-level mechanism is not disclosed in the NVD description. Insufficient technical detail is available to name specific functions, system calls, or parameters. However, the described behavior is consistent with a kernel syscall/invoke-path input validation flaw, where a pointer, length, or other user-controlled value is not properly checked against the calling task's memory region boundaries before being dereferenced or used in a privileged operation. This allows an unprivileged task to craft an input that references privileged memory regions (such as the kernel's own data section or other tasks' memory), defeating the memory protection imposed by the MPU.

The CVSS vector reflects this impact: AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H. The attack is local (AV:L), requires only low attack complexity (AC:L), and needs only low privileges (PR:L) — the unprivileged task already running on the device. No user interaction is required (UI:N). The scope is changed (S:C) because a compromise of the kernel (the vulnerable component) allows full control of the entire system beyond the initial task. The impact on confidentiality, integrity, and availability is High (C:H/I:H/A:H).

Given the EPSS score of 0.00114 (1.6% percentile), this vulnerability is not currently being actively exploited in the wild per EPSS data, and it is not listed on CISA's Known Exploited Vulnerabilities (KEV) catalog. However, the absence of public exploit code does not diminish the severity — the vulnerability class is well understood, and the conditions (MPU enabled) are documented and reachable.

Exploitation Scenarios

Important caveat: No public PoC or exploit code is available. The attack chain described below is inferred from the vulnerability class and the CVE description, not from specific observed exploits.

Attack Chain Steps

1. Reconnaissance / Target Identification

The attacker requires local access to a device running FreeRTOS-Kernel with MPU-enabled ports. In a typical scenario, the attacker already has the ability to execute an arbitrary unprivileged task on the device. This could be achieved through:

• A prior vulnerability in an application-level task (e.g., a network-facing service parsing malicious input).
• Physical access to the device allowing firmware modification or task injection via debug interfaces.
• A supply chain compromise providing a malicious application package.

The attacker first identifies the FreeRTOS version running on the target (via firmware analysis, version strings in memory, or known device fingerprints) to confirm it is before 11.3.1 and that MPU support is compiled in.

2. Triggering the Flaw

The attacker crafts a malicious task (or modifies an existing task's code) that invokes a kernel service while passing intentionally malformed or out-of-bounds input. Because the kernel does not adequately validate this input on MPU-enabled ports, the kernel enters a state where it trusts the attacker-controlled data. The specific system call or API used is not disclosed in the NVD description; only the class of flaw (improper input validation) is known.

At a class level, the trigger involves:

• The attacker's task calling a kernel API and supplying an argument — such as a buffer pointer, size, or task handle — that points to kernel memory or that causes the kernel to write outside the expected memory boundaries.
• The kernel, lacking proper validation, dereferences this input or uses it to update its own structures, thereby executing with elevated privileges.

3. Payload / Execution Method

The payload is delivered as part of the malformed input. The attacker's goal is to achieve arbitrary code execution in privileged (kernel) context. The likely mechanism is:

• Memory corruption / arbitrary write: The attacker supplies an unchecked pointer that the kernel writes to, allowing the attacker to overwrite kernel data structures (e.g., a function pointer, task control block, or exception vector).
• Privilege escalation: After corrupting the kernel context, the attacker redirects execution to their own code running in privileged mode. This code can then disable memory protection, modify any task's state, or directly interact with the hardware.

4. Post-Exploitation Impact

With code execution in kernel context, the attacker can:

• Read and write all system memory, including other tasks' secrets (credentials, cryptographic keys, sensor data).
• Modify the scheduler and any running task, causing denial of service (crash, hang).
• Persist by modifying the firmware or boot process if flash write access is available.
• Pivot to network attacks using the device's communication interfaces with elevated privilege.
• On multi-tenant or multi-application devices (e.g., a smart home hub hosting multiple apps), the attacker could compromise the entire platform.

Realistic attack chain summary: Application-level compromise → load unprivileged task → trigger improper input validation during kernel syscall → escalate to privileged context → full device takeover.

Impact Assessment

Business Impact:

• Confidentiality: High (C:H) — the attacker can read all kernel and user memory after escalation, including encryption keys, credentials, and sensitive sensor data.
• Integrity: High (I:H) — the attacker can modify kernel memory, disable security features, and alter running tasks.
• Availability: High (A:H) — the attacker can crash the kernel, corrupt critical structures, or brick the device.
• Scope: Changed (S:C) — the initial compromise of the unprivileged task extends to the entire system, bypassing the isolation provided by the MPU.

Affected Systems:

• All FreeRTOS-Kernel versions before 11.3.1 that are compiled with MPU support enabled.
• Devices include: IoT sensors, smart meters, medical devices, industrial controllers, consumer electronics (smart home hubs, wearables), automotive ECUs, and other embedded systems.
• The exact list of affected hardware/ports is not provided in the NVD description, but any MPU-enabled port is implicated.

Blast Radius:

• A single unprivileged task compromise leads to full kernel compromise, enabling lateral movement to all other tasks on the device (there is typically no further "network lateral movement" on a single MCU, but the device's overall function is compromised).
• Supply chain risk: devices deployed in critical infrastructure (power grids, medical networks, industrial automation) could be remotely compromised if the initial unprivileged execution comes from a network-exposed application.
• Regulatory impact: for medically approved or safety-certified devices, a vulnerability of this class may require field-level firmware updates and re-certification.

CVSS Subscores (derived from the vector):

• Attack Vector: Local (physical or logical local access)
• Attack Complexity: Low (no special conditions needed)
• Privileges Required: Low (an unprivileged task)
• User Interaction: None
• Scope: Changed

Detection Guidance

The detection rules below are generic and focus on the observable behaviors associated with exploiting an input validation flaw in a kernel context on an MPU-enabled embedded system. Because this is a local, embedded vulnerability without a network signature, the rules target firmware analysis, memory inspection, and host-based monitoring where such visibility exists.

Sigma Rule

title: FreeRTOS Kernel Privilege Escalation - Unusual Memory Access Patterns
id: 2c8ec54b-9279-4e4a-9bf0-7d4ae8c9abd1
status: experimental
description: Detects anomalous behavior on FreeRTOS MPU-enabled systems indicative of improper input validation leading to privileged execution (CVE-2026-77234)
author: Valtersit Threat Intelligence
date: 2026/05/15
logsource:
    category: process_creation
    product: freertos
detection:
    selection:
        EventID: 1
        Integrity|contains: 
            - 'MPU'
            - 'privilege'
    condition: selection
falsepositives:
    - Legitimate kernel extensions
    - System maintenance tasks
level: critical

YARA Rule

rule FreeRTOS_Kernel_CVE_2026_77234_Privilege_Escalation
{
    meta:
        author = "Valtersit Threat Intelligence"
        description = "Detects firmware or binary artifacts containing FreeRTOS-Kernel with MPU enabled and versions prior to 11.3.1"
        cve = "CVE-2026-77234"
        version = "1.0"
    strings:
        $freertos = "FreeRTOS" ascii
        $mpu_enabled = "configENABLE_MPU" ascii
        $version_before = "V11.0" ascii
        $version_before2 = "V11.1" ascii
        $version_before3 = "V11.2" ascii
        $version_before4 = "V11.3.0" ascii
        $kernel_path = "kernel" ascii
    condition:
        $freertos and $mpu_enabled and ($version_before or $version_before2 or $version_before3 or $version_before4)
}

Suricata IDS Rule

alert tcp any any -> any any (msg:"FREERTOS CVE-2026-77234 Potential Privilege Escalation Attempt - Unusual Task Behavior"; flow:established,to_server; content:"|00|"; metadata:cve "CVE-2026-77234"; classtype:attempted-admin; sid:8772341; rev:1;)

Note: A network-based signature for this local vulnerability is not practically reliable. This rule is a placeholder placeholder for packet captures that may carry task scheduling messages if the RTOS traffic is passed over an IP network. In practice, detection should rely on host-based monitoring and firmware audits.

Elastic Detection

// EQL rule for detecting anomalous memory access on FreeRTOS MPU systems
// Assumes filebeat or winlogbeat capturing system calls or memory protection events
sequence by process.entity_id
    [file where event.module == "freertos" and process.name == "kernel" and message like "*prvTaskExitError*"]
    [process where event.action == "mem_protection" and code == 6 and message like "*kernel*"]

Splunk SPL Query

index=embedded_rtos sourcetype=freertos_logs
| where "configENABLE_MPU" AND ("version" < "11.3.1")
| eval exploit_indicator = if(searchmatch("*privilege*") OR searchmatch("*MPU fault*") OR searchmatch("*unexpected task exit*"), "HIGH", "NORMAL")
| where exploit_indicator == "HIGH"
| table _time, host, task_name, privilege_level, fault_address
| stats count by host, task_name

Wazuh OSSEC Rule

<group name="freertos,">
    <rule id="951604" level="12">
        <decoded_as>json</decoded_as>
        <field name="rtos_version">\.*11\.[0-3]\.\d+\.*</field>
        <field name="mpu_enabled">true</field>
        <match>mem_protection_fault</match>
        <description>FreeRTOS-Kernel MPU fault detected - potential CVE-2026-77234 exploitation</description>
        <group>privilege_escalation,</group>
        <mitre>
            <id>T1068</id>
        </mitre>
    </rule>
</group>

Note on detection: Given the embedded nature of FreeRTOS deployments, observability is often limited. For most deployments, the highest-value detection comes from firmware/binary scanning (to identify vulnerable versions in the field) and hardware-level memory protection monitoring (MPU fault exceptions indicating out-of-bounds access attempts). Additionally, manufacturers should monitor for unexpected task exits, system crashes, or watchdog timeouts that may indicate exploitation attempts.

Mitigation & Patch Guidance

Patch Confidence: 2/4 — CLAIMED. The patch is claimed by a single source (NVD refers to the fix with "upgrade to version 11.3.1 or later"). It is not yet independently confirmed by multiple sources, and no vendor advisory (Amazon/AWS) has been published at the time of this report. Proceed with caution; verify the fix against your exact build configuration.

Immediate Mitigations

1. Upgrade FreeRTOS-Kernel to 11.3.1 or later as soon as the source code is available and validation is complete. This is the only known remediation.
2. Disable MPU support if not strictly required. If the system does not rely on hard memory isolation between tasks, rebuilding the kernel without configENABLE_MPU can eliminate the vulnerable path. Assess the security trade-off: losing MPU protection may increase risk from other task-level flaws.
3. Harden application-layer inputs. Since the attack chain begins with an unprivileged task, review all tasks that accept external input (network, serial, file) for buffer overflows, format string issues, and other injection flaws. This reduces the likelihood an attacker can reach the vulnerable kernel path.
4. Restrict physical access to devices where feasible, as the attack requires local code execution.

Patch / Upgrade Steps

1. Obtain the patched FreeRTOS-Kernel source (version 11.3.1 or later) from the official FreeRTOS repository (GitHub: FreeRTOS/FreeRTOS-Kernel).
2. Validate the patch against your system configuration:
   • Check that your MPU port is compatible with the new kernel version.
   • Run your full test suite, especially memory protection tests and port-specific regression tests.
3. Rebuild the kernel and re-flash all affected devices. Plan for over-the-air (OTA) updates if supported by your hardware.
4. After deployment, verify the kernel version and run a functional test of the MPU features.

Long-Term Hardening

1. Adopt an SBOM (Software Bill of Materials) for all firmware components. Automated SBOM tooling allows continuous scanning for new vulnerabilities in FreeRTOS and other embedded components.
2. Establish a rapid patching process for embedded devices, including the ability to push OTA updates. Many deployments remain unpatched for years due to manual update processes.
3. Monitor vendor advisories from Amazon AWS (FreeRTOS is now managed under AWS IoT) for updates on this CVE and related issues.
4. Apply the principle of least privilege to tasks in the FreeRTOS system design. Reduce the number of tasks running with elevated permissions and ensure the kernel's MPU region definitions are minimal and correct.
5. Integrate security testing into the CI/CD pipeline for firmware development, including static analysis (e.g., checking for use of untrusted inputs in privileged paths) and fuzzing of kernel API calls.

References

1. NVD Entry: https://nvd.nist.gov/vuln/detail/CVE-2026-77234 — Official NVD record containing the description and CVSS vector.
2. FreeRTOS-Kernel GitHub Repository: https://github.com/FreeRTOS/FreeRTOS-Kernel — Source code repository where version 11.3.1 (containing the fix) can be retrieved. Release notes for the fix should be reviewed.
3. FreeRTOS Official Website: https://www.freertos.org/ — General documentation, including MPU support details and upgrade guides.
4. CWE-863 (Incorrect Authorization): https://cwe.mitre.org/data/definitions/863.html — Common Weakness Enumeration entry describing the underlying weakness class.
5. CISA Known Exploited Vulnerabilities Catalog: https://www.cisa.gov/known-exploited-vulnerabilities-catalog — Confirmation that this CVE is not currently listed in the KEV, indicating no known exploitation in the wild at the time of writing.

Threat Actor Intelligence: No known threat actor campaigns are associated with this CVE at the time of publication. The EPSS score (0.00114, 1.6th percentile) and absence from CISA KEV indicate that exploitation is not yet observed or widespread. However, given the prevalence of FreeRTOS in critical embedded infrastructure and the high severity rating, this CVE should be actively watched.

Report Disclaimer: This report is based on the NVD description and provided metadata only. Specific implementation details (function names, exact trigger conditions) are unavailable from the public description.