Kernel Pipe Re-initialization Flaw in Zephyr OS

Executive Summary

CVE-2026-10671 is a vulnerability in the Zephyr RTOS kernel's pipe implementation. In versions 4.1.0 through 4.4.0 with CONFIG_USERSPACE enabled, the userspace syscall verifier z_vrfy_k_pipe_init() incorrectly used K_SYSCALL_OBJ() instead of K_SYSCALL_OBJ_NEVER_INIT(). This allowed an unprivileged user thread with access to a k_pipe object to re-initialize a pipe that was already in use.

When a pipe is re-initialized, the function z_impl_k_pipe_init() unconditionally resets the ring buffer, clears the waiting count, and re-initializes the wait queues without waking or accounting for threads already blocked on the pipe. This leaves threads waiting in k_pipe_read() or k_pipe_write() orphaned, with their wait queue pointers pointing to invalid or re-initialized structures.

When these orphaned threads are later woken or timed out, the scheduler attempts to remove them from the corrupted wait queues, leading to invalid memory writes through stale pointers. This causes kernel wait-queue corruption, lost wakeups, indefinitely blocked threads, and potential data loss.

The fix involves changing the verifier to use K_SYSCALL_OBJ_NEVER_INIT(), which prevents re-initialization of an already-initialized pipe, aligning it with the behavior of other kernel objects like message queues.

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Detection Guidance

Detecting this vulnerability requires checking if your Zephyr RTOS system is running a vulnerable version (4.1.0 through 4.4.0) with CONFIG_USERSPACE enabled. Since this is a kernel-level flaw, detection involves verifying the Zephyr version and configuration rather than network-based scanning.

• Check the Zephyr RTOS version: Run `west --version` or inspect the Zephyr build configuration to confirm the version. If it is between 4.1.0 and 4.4.0, the system may be vulnerable.
• Verify if CONFIG_USERSPACE is enabled: Inspect the build configuration file (usually `prj.conf` or `zephyr/.config`) for `CONFIG_USERSPACE=y`. If this flag is present, the system is at risk.
• Review kernel logs for signs of pipe re-initialization or wait queue corruption: Look for anomalies like orphaned threads, kernel panics, or unexpected scheduler behavior. However, these may not always be visible without deep kernel debugging.

There are no direct network-based detection methods for this vulnerability, as it is a local privilege escalation flaw in the kernel's pipe implementation.

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Impact Analysis

This vulnerability can impact you in several ways if you are using Zephyr RTOS versions 4.1.0 through 4.4.0 with CONFIG_USERSPACE enabled:

• Kernel wait-queue corruption: The vulnerability can corrupt kernel wait queues, leading to unpredictable system behavior, crashes, or instability.
• Lost wakeups: Threads waiting on a pipe may never be woken, causing them to hang indefinitely and disrupting application functionality.
• Indefinitely blocked threads: Applications relying on pipes for inter-thread communication may experience deadlocks or unresponsive behavior.
• Silent data loss: Data written to or read from pipes may be lost without any indication, leading to incorrect or incomplete data processing.
• Privilege escalation risk: An unprivileged user thread could exploit this flaw to corrupt kernel structures, potentially leading to further privilege escalation or unauthorized access to system resources.

The impact is particularly severe in systems where pipes are used for critical inter-thread or inter-process communication, as the corruption can propagate and affect multiple components.

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Compliance Impact

This vulnerability can affect compliance with common standards and regulations in the following ways:

• GDPR (General Data Protection Regulation): If the Zephyr RTOS is used in a system processing personal data, the vulnerability could lead to data loss or corruption, potentially violating GDPR's requirements for data integrity and availability. Additionally, if the vulnerability is exploited to gain unauthorized access to personal data, it could result in a data breach, triggering GDPR's breach notification and remediation obligations.
• HIPAA (Health Insurance Portability and Accountability Act): In healthcare applications, if the Zephyr RTOS is used to process or transmit protected health information (PHI), the vulnerability could compromise the integrity and availability of PHI. HIPAA requires safeguards to ensure the confidentiality, integrity, and availability of PHI, and this vulnerability could lead to non-compliance if exploited.
• Other standards (e.g., ISO 27001, NIST SP 800-53): The vulnerability could impact compliance with security standards that require secure system design, integrity protection, and availability. For example, ISO 27001 mandates controls for system integrity and availability, while NIST SP 800-53 includes requirements for access control and system integrity. Exploitation of this vulnerability could violate these controls.

Overall, the vulnerability undermines the security and reliability of systems using the affected Zephyr RTOS versions, which could lead to non-compliance with regulations and standards that require robust security measures to protect sensitive data and ensure system availability.

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Mitigation Strategies

To mitigate CVE-2026-10671, follow these steps:

• Apply the official patch: Update Zephyr RTOS to the latest version (4.5.0 or later) or apply the backported fix to versions 4.4, 4.3, or 3.7. The patch replaces `K_SYSCALL_OBJ()` with `K_SYSCALL_OBJ_NEVER_INIT()` in the `z_vrfy_k_pipe_init()` function.
• If patching is not immediately possible, disable CONFIG_USERSPACE: Rebuild Zephyr without `CONFIG_USERSPACE=y` to eliminate the attack surface. Note that this may break applications relying on userspace features.
• Restrict access to k_pipe objects: Limit the number of unprivileged threads with access to pipe objects until the system is patched. This reduces the risk of exploitation but does not fully mitigate the flaw.
• Monitor for suspicious activity: Watch for signs of kernel corruption, such as unexpected thread blocks, lost wakeups, or system instability. These may indicate exploitation attempts.

The most effective mitigation is applying the patch, as it directly addresses the root cause of the vulnerability.

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