CVE-2025-5867: RT-Thread Null Pointer Dereference Flaw

CVE-2025-5867 Overview

A critical vulnerability has been identified in RT-Thread version 5.1.0, affecting the csys_sendto function within the lightweight process (LWP) syscall implementation. This null pointer dereference vulnerability exists in the file rt-thread/components/lwp/lwp_syscall.c and can be triggered through manipulation of the argument parameter, potentially leading to system instability or denial of service conditions on affected embedded systems.

RT-Thread is a popular open-source real-time operating system designed for embedded devices and IoT applications. The LWP (Lightweight Process) subsystem provides process management capabilities similar to traditional operating systems, making this vulnerability particularly concerning for deployed IoT infrastructure.

Critical Impact

Attackers with adjacent network access and low-level privileges can trigger a null pointer dereference in the RT-Thread kernel, potentially crashing the system or causing denial of service on embedded devices and IoT systems running RT-Thread 5.1.0.

Affected Products

• RT-Thread 5.1.0
• Systems running RT-Thread RTOS with LWP syscall functionality enabled
• IoT and embedded devices utilizing RT-Thread's lightweight process implementation

Discovery Timeline

• June 9, 2025 - CVE-2025-5867 published to NVD
• July 11, 2025 - Last updated in NVD database

Technical Details for CVE-2025-5867

Vulnerability Analysis

This vulnerability is classified under CWE-476 (NULL Pointer Dereference) and CWE-404 (Improper Resource Shutdown or Release). The flaw resides in the csys_sendto function, which is part of the LWP syscall interface that handles socket-related system calls in RT-Thread.

When the csys_sendto function processes a malformed or specially crafted argument, it fails to properly validate the pointer before dereferencing it. This lack of input validation allows an attacker to trigger a null pointer dereference condition, which in an embedded RTOS environment typically results in a system crash or undefined behavior.

The vulnerability requires adjacent network access, meaning an attacker must be on the same network segment or have local network proximity to the target device. While low-level privileges are required to exploit this vulnerability, the impact is significant given that embedded systems and IoT devices often cannot easily recover from kernel-level crashes without manual intervention.

Root Cause

The root cause of this vulnerability is inadequate input validation in the csys_sendto syscall handler. The function fails to verify that the to argument parameter contains a valid, non-null pointer before attempting to dereference it. In RTOS environments like RT-Thread, syscall handlers must rigorously validate all user-provided parameters since a crash in kernel space typically halts the entire system.

The improper resource handling (CWE-404) aspect suggests that the vulnerability may also involve failure to properly manage socket resources when invalid parameters are encountered, potentially leaving resources in an inconsistent state.

Attack Vector

The attack vector is through the adjacent network, requiring the attacker to have proximity to the target system. Exploitation involves:

1. Gaining access to a network segment where vulnerable RT-Thread devices are deployed
2. Authenticating with low-level privileges to the target system
3. Invoking the csys_sendto syscall with a specially crafted null or invalid pointer argument
4. The kernel fails to validate the argument and attempts to dereference the null pointer
5. System crash or denial of service occurs

The vulnerability mechanism involves the csys_sendto function in rt-thread/components/lwp/lwp_syscall.c failing to validate pointer arguments before use. When a null or invalid pointer is passed as the destination address argument, the kernel attempts to access memory at an invalid location, triggering a null pointer dereference exception. In embedded systems without memory protection, this typically results in immediate system failure. Technical details and discussion are available in the GitHub Issue Discussion.

Detection Methods for CVE-2025-5867

Indicators of Compromise

• Unexpected system crashes or reboots of RT-Thread devices, particularly those with LWP functionality enabled
• Kernel panic or hard fault logs indicating null pointer exceptions in the lwp_syscall.c module
• Anomalous network activity targeting RT-Thread devices from adjacent network segments
• System logs showing repeated syscall failures related to socket operations

Detection Strategies

• Monitor embedded device health metrics for unexpected reboots or crashes that may indicate exploitation attempts
• Implement network segmentation monitoring to detect unauthorized access attempts to IoT device network segments
• Review system logs for fault handlers being triggered in the LWP syscall path
• Deploy intrusion detection systems configured to monitor traffic patterns to embedded devices

Monitoring Recommendations

• Enable verbose logging for the LWP subsystem where possible to capture syscall argument validation failures
• Implement watchdog mechanisms to detect and report system crashes for forensic analysis
• Monitor network traffic for unusual patterns targeting RT-Thread devices on adjacent network segments
• Establish baseline behavior for embedded devices to identify anomalous crash patterns

How to Mitigate CVE-2025-5867

Immediate Actions Required

• Inventory all systems running RT-Thread 5.1.0 to identify vulnerable deployments
• Implement network segmentation to restrict access to RT-Thread devices from untrusted network segments
• Review and restrict user privileges on RT-Thread systems to minimize attack surface
• Monitor affected devices for signs of exploitation or unusual crash patterns

Patch Information

At the time of publication, patch information should be obtained from the official RT-Thread project. Organizations are advised to monitor the RT-Thread GitHub repository for updates and security patches addressing this vulnerability. The VulDB entry may also contain updated remediation information.

Workarounds

• Disable the LWP subsystem if not required for your application to eliminate the vulnerable code path
• Implement strict network access controls to prevent unauthorized adjacent network access to RT-Thread devices
• Apply principle of least privilege to limit the number of users with syscall access
• Deploy application-level input validation where possible before syscall invocation
• Consider firmware rollback to a previous version if confirmed unaffected, pending official patch release

Pending official patches, administrators should implement compensating controls through network-level restrictions. Consult the GitHub issue discussion for community-provided mitigations and patch status updates.