CVE-2026-40337: Sentry Kernel DoS Vulnerability

CVE-2026-40337 Overview

CVE-2026-40337 is a vulnerability affecting the Sentry kernel, a high security level micro-kernel implementation designed for high security embedded systems. The vulnerability exists in the __sys_int_* syscall family, where tasks with DEV or IO capability can improperly interact with another task's IRQ line. This improper access control can lead to denial of service conditions and enable covert-channels between the vulnerable task and external entities.

Critical Impact

Tasks with elevated device capabilities can manipulate IRQ lines belonging to other tasks, potentially causing system instability and enabling unauthorized communication channels in high-security embedded environments.

Affected Products

• Sentry kernel versions prior to 0.4.7
• Embedded systems utilizing Sentry kernel with DEV or IO capability tasks
• High security embedded deployments running vulnerable kernel versions

Discovery Timeline

• 2026-04-18 - CVE CVE-2026-40337 published to NVD
• 2026-04-20 - Last updated in NVD database

Technical Details for CVE-2026-40337

Vulnerability Analysis

The vulnerability stems from CWE-283 (Unverified Ownership), where the Sentry kernel fails to properly verify that the task invoking interrupt-related syscalls actually owns the target IRQ line. The __sys_int_* syscall family, which includes functions for acknowledging, enabling, and disabling interrupts, does not validate that the calling task is the legitimate owner of the specified interrupt before performing operations on it.

In a properly secured micro-kernel architecture, hardware interrupt lines should be strictly isolated between tasks to maintain security boundaries. However, prior to version 0.4.7, any task possessing either the DEV (device) or IO (input/output) capability could invoke these syscalls to interact with IRQ lines assigned to other tasks. This breaks the fundamental isolation guarantees expected from a security-focused micro-kernel.

The impact manifests in two primary ways: first, a malicious or compromised task can disable or manipulate interrupt handlers belonging to other tasks, causing denial of service. Second, the ability to acknowledge interrupts belonging to other tasks creates a potential covert channel that could be exploited to exfiltrate data or coordinate between processes that should be isolated.

Root Cause

The root cause is missing ownership verification in the interrupt-related syscall handlers. The kernel code retrieved the owner of the specified IRQ but did not compare it against the currently executing task before allowing the operation to proceed. This allowed any task with sufficient capability flags to perform interrupt operations on IRQ lines they did not own.

Attack Vector

The attack requires local access and high privileges (DEV or IO capability). An attacker controlling a task with device or IO capabilities can craft syscalls targeting IRQ numbers assigned to other tasks. By disabling another task's interrupt handler, the attacker can prevent that task from responding to hardware events, causing denial of service. Alternatively, by manipulating interrupt acknowledgment, the attacker can establish timing-based covert channels between isolated security domains.

         /* user interrupt with no owning task. Should not happen as the kernel do not hold any IRQ */
         panic(PANIC_KERNEL_INVALID_MANAGER_RESPONSE);
     }
+    if (unlikely(owner != current)) {
+        /* device associated IRQ is not owned by the current task */
+        mgr_task_set_sysreturn(current, STATUS_DENIED);
+        goto end;
+    }
     /* push the inth event into the task input events queue */
-    if (unlikely(mgr_interrupt_acknowledge_irq(IRQn) == K_STATUS_OKAY)) {
+    if (unlikely(mgr_interrupt_acknowledge_irq(IRQn) != K_STATUS_OKAY)) {
         /* should not rise while IRQ ownership has been checked! see dts file */
         panic(PANIC_KERNEL_INVALID_MANAGER_RESPONSE);
     }

Source: GitHub Commit Update

Detection Methods for CVE-2026-40337

Indicators of Compromise

• Unexpected STATUS_DENIED return values from interrupt-related syscalls in task logs
• System instability or unresponsive hardware components due to disabled interrupt handlers
• Unusual patterns in interrupt acknowledgment timing that could indicate covert channel activity
• Tasks attempting to access IRQ numbers outside their assigned range

Detection Strategies

• Monitor syscall activity for tasks with DEV or IO capabilities, flagging attempts to interact with IRQs not assigned to them
• Implement kernel-level auditing for all __sys_int_* syscall invocations with cross-reference to IRQ ownership tables
• Deploy behavioral analysis to detect anomalous interrupt manipulation patterns
• Enable verbose kernel logging to capture interrupt-related operations for forensic analysis

Monitoring Recommendations

• Establish baseline interrupt handling patterns for each task and alert on deviations
• Monitor system stability metrics that could indicate DoS conditions from interrupt manipulation
• Track capability assignments and audit tasks holding DEV or IO privileges
• Implement real-time alerting for repeated failed interrupt operations that return STATUS_DENIED

How to Mitigate CVE-2026-40337

Immediate Actions Required

• Upgrade Sentry kernel to version 0.4.7 or later immediately
• Audit all tasks currently configured with DEV or IO capabilities
• Reduce the number of tasks with DEV and IO capabilities to the minimum necessary
• Review system configuration to consolidate device access to a single trusted task where possible

Patch Information

A security patch is available in Sentry kernel version 0.4.7. The fix adds proper ownership verification in the interrupt syscall handlers, ensuring that only the task that owns a specific IRQ can perform operations on it. The patch modifies multiple syscall gate files including sysgate_int_acknowledge.c and sysgate_int_disable.c to check that the owner matches current before allowing the operation. If ownership verification fails, the syscall now returns STATUS_DENIED instead of proceeding with the operation. For detailed patch information, see the GitHub Security Advisory GHSA-5hgv-rg2f-79pg and the associated pull request.

Workarounds

• Reduce tasks that have the DEV and IO capability to a single task, eliminating the possibility of cross-task IRQ manipulation
• Implement strict capability assignment policies limiting DEV and IO to only essential tasks
• Consider architectural changes to consolidate all device interactions through a single trusted driver task
• Deploy additional monitoring and access controls at the application layer to detect abuse

# Configuration example
# Review and restrict capability assignments in your Sentry kernel configuration
# Limit DEV and IO capabilities to essential tasks only

# Example: Audit current capability assignments
# Check your device tree source (dts) files for capability configurations
# Ensure only one task holds DEV/IO capabilities where possible

# After patching, verify the fix is active:
# Check kernel version is 0.4.7 or later
# Monitor for STATUS_DENIED returns indicating the ownership check is working