CVE-2025-5866: RT-Thread Buffer Overflow Vulnerability

CVE-2025-5866 Overview

A critical vulnerability has been identified in RT-Thread version 5.1.0, affecting the sys_sigprocmask function within the file rt-thread/components/lwp/lwp_syscall.c. The vulnerability stems from improper validation of an array index through manipulation of the how argument, which can lead to memory corruption and potential code execution.

RT-Thread is a popular open-source real-time operating system (RTOS) designed for embedded systems and IoT devices. This vulnerability in the lightweight process (LWP) syscall component poses significant risks to embedded systems relying on RT-Thread for their operations.

Critical Impact

Attackers with adjacent network access and low privileges can exploit improper array index validation to achieve high confidentiality, integrity, and availability impact on affected RT-Thread systems.

Affected Products

• RT-Thread 5.1.0
• RT-Thread LWP (Lightweight Process) component
• Systems using lwp_syscall.c signal handling functions

Discovery Timeline

• June 9, 2025 - CVE-2025-5866 published to NVD
• July 11, 2025 - Last updated in NVD database

Technical Details for CVE-2025-5866

Vulnerability Analysis

This vulnerability is classified under CWE-129 (Improper Validation of Array Index) and CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer). The flaw exists in the signal processing mechanism of RT-Thread's lightweight process subsystem.

The sys_sigprocmask function is responsible for managing process signal masks, which control how signals are handled by a process. When the how argument is provided without proper bounds checking, an attacker can supply an out-of-bounds value that causes the function to access memory outside the intended array boundaries.

The vulnerability requires adjacent network access and low-privilege authentication to exploit, making it particularly concerning for networked embedded systems and IoT devices where RT-Thread is commonly deployed. Successful exploitation can result in complete compromise of system confidentiality, integrity, and availability.

Root Cause

The root cause of this vulnerability lies in the insufficient validation of the how parameter passed to the sys_sigprocmask function. In signal mask operations, the how parameter typically accepts values like SIG_BLOCK, SIG_UNBLOCK, or SIG_SETMASK to determine how the signal mask should be modified.

The implementation fails to properly validate that the how argument falls within the expected range of valid values before using it as an array index or in switch-case logic. This allows an attacker to provide arbitrary values that result in out-of-bounds memory access, potentially corrupting adjacent memory structures or leaking sensitive information.

Attack Vector

The attack requires adjacent network access, meaning the attacker must be on the same network segment as the vulnerable system. With low-privilege access to the RT-Thread system, an attacker can invoke the sys_sigprocmask syscall with a maliciously crafted how parameter value.

The exploitation flow involves:

1. Establishing a connection to the RT-Thread system from an adjacent network
2. Authenticating with low-privilege credentials
3. Invoking the sys_sigprocmask syscall with an out-of-bounds how value
4. Triggering improper array index access leading to memory corruption

The vulnerability mechanism exists within the syscall handler for signal mask operations. When the how parameter is processed without bounds validation, the system may access or modify memory outside intended boundaries. For detailed technical information, refer to the GitHub Issue Discussion.

Detection Methods for CVE-2025-5866

Indicators of Compromise

• Unexpected crashes or restarts in RT-Thread-based embedded systems
• Abnormal syscall patterns involving sys_sigprocmask with unusual parameter values
• Memory corruption errors or segmentation faults in the LWP subsystem
• Suspicious network activity from adjacent hosts targeting RT-Thread services

Detection Strategies

• Monitor syscall activity for sys_sigprocmask calls with parameter values outside the valid range (typically 0-2 for standard signal mask operations)
• Implement runtime bounds checking on embedded systems to detect out-of-bounds memory access attempts
• Deploy network monitoring to identify unusual traffic patterns from adjacent network segments targeting RT-Thread devices
• Enable logging for LWP subsystem operations to capture anomalous behavior

Monitoring Recommendations

• Configure system logging to capture all syscall operations in the LWP component
• Implement memory protection mechanisms such as stack canaries and address space layout randomization (ASLR) where supported
• Deploy network segmentation to limit adjacent network access to critical embedded systems
• Establish baseline behavior for normal RT-Thread operations to detect deviations

How to Mitigate CVE-2025-5866

Immediate Actions Required

• Identify all RT-Thread 5.1.0 deployments in your environment
• Implement network segmentation to isolate affected embedded systems from untrusted adjacent networks
• Apply input validation controls at the application layer to filter syscall parameters
• Monitor the RT-Thread GitHub repository for official patches and updates

Patch Information

At the time of publication, users should monitor the official RT-Thread project for security updates. The vulnerability has been disclosed through the GitHub Issue #10300, and additional details are available through VulDB.

Organizations should subscribe to RT-Thread security announcements and apply patches as soon as they become available. In the interim, implement the workarounds described below to reduce exposure.

Workarounds

• Restrict adjacent network access to RT-Thread systems using network access control lists (ACLs) and firewalls
• Implement additional authentication requirements for accessing RT-Thread services
• Apply application-level input validation to sanitize syscall parameters before processing
• Consider disabling unnecessary LWP functionality if signal mask operations are not required for your use case

# Network isolation example for embedded systems
# Restrict access to RT-Thread device from adjacent networks
iptables -A INPUT -i eth0 -s 192.168.1.0/24 -j DROP
iptables -A INPUT -i eth0 -s trusted_host_ip -j ACCEPT

# Implement additional logging for syscall monitoring
# Consult RT-Thread documentation for enabling debug logging
# RT_DEBUG_LOG=1 in rtconfig.h for development environments