CVE-2025-6693

Executive Summary

CVE-2025-6693 is a critical memory corruption vulnerability discovered in the RT-Thread real-time operating system, affecting versions up to and including 5.1.0. The flaw resides in the core device driver file components/drivers/core/device.c, specifically within the functions sys_device_open, sys_device_read, sys_device_control, sys_device_init, sys_device_close, and sys_device_write. An attacker with local access can exploit this vulnerability to corrupt memory, potentially leading to arbitrary code execution, denial of service, or privilege escalation. The vendor (RT-Thread) was contacted but did not respond, and no official patch is currently available. This vulnerability poses a significant risk to embedded systems, IoT devices, and industrial control systems that rely on RT-Thread.

Supply Chain & Package Security

RT-Thread is a widely used open-source real-time operating system, often integrated into embedded and IoT products. The lack of a vendor response and the absence of a patch create a supply chain risk. Organizations using RT-Thread in their products must assess their exposure and consider alternative mitigations, such as disabling the vulnerable device driver functions or applying strict access controls. The vulnerability is not related to any package manager (NPM, PyPI, Go, Ruby) but is a core OS component.

CVSS Breakdown & Threat Level

The CVSS score is listed as 0.0, which is likely a placeholder or uncalculated. Based on the description and impact, a reasonable CVSS v3.1 vector would be:

• Attack Vector (AV): Local (L) – Requires local access to the system.
• Attack Complexity (AC): Low (L) – The vulnerability is straightforward to exploit.
• Privileges Required (PR): Low (L) – The attacker needs some level of access, but not necessarily root.
• User Interaction (UI): None (N) – No user interaction is required.
• Scope (S): Unchanged (U) – The vulnerability affects only the vulnerable component.
• Confidentiality (C): High (H) – Memory corruption can lead to data leakage.
• Integrity (I): High (H) – Memory corruption can allow data modification.
• Availability (A): High (H) – Memory corruption can cause system crashes.

Estimated CVSS Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H Estimated Base Score: 7.8 (High)

Threat Level: High. The vulnerability is critical due to the potential for full system compromise, but the local attack vector reduces the immediate risk for internet-facing systems.

Deep Dive & Mechanics

The vulnerability is located in the RT-Thread device driver framework, specifically in the file components/drivers/core/device.c. The functions sys_device_open, sys_device_read, sys_device_control, sys_device_init, sys_device_close, and sys_device_write are part of the system call interface for device operations. The exact nature of the memory corruption is not publicly detailed, but it likely involves one or more of the following:

• Buffer Overflow: Insufficient bounds checking when copying data to or from device buffers.
• Use-After-Free: Improper handling of device object lifetimes, leading to access after deallocation.
• Integer Overflow: Arithmetic errors in size calculations leading to undersized buffer allocations.
• Null Pointer Dereference: Lack of validation on device pointers or function pointers.

The manipulation of these functions can corrupt kernel memory, leading to arbitrary code execution in kernel space. Since RT-Thread is a real-time OS, memory corruption can also cause unpredictable behavior, system hangs, or crashes.

Vulnerable vs. Patched Code

Since no official patch is available, a direct comparison is not possible. However, based on common memory corruption patterns, the vulnerable code likely lacks proper input validation and bounds checking. A hypothetical patched version would include:

• Input Validation: Check that device pointers are not NULL and that device IDs are within valid ranges.
• Bounds Checking: Ensure that read/write operations do not exceed allocated buffer sizes.
• Safe Memory Functions: Use functions like memcpy_s or strncpy instead of memcpy or strcpy.
• Locking Mechanisms: Properly synchronize access to shared device structures to prevent race conditions.

Example of vulnerable code (hypothetical):

// Vulnerable: No bounds checking
int sys_device_read(rt_device_t dev, rt_off_t pos, void *buffer, rt_size_t size) {
    if (dev->read) {
        return dev->read(dev, pos, buffer, size);
    }
    return -RT_ERROR;
}

Example of patched code (hypothetical):

// Patched: Added bounds checking
int sys_device_read(rt_device_t dev, rt_off_t pos, void *buffer, rt_size_t size) {
    if (dev == RT_NULL || buffer == RT_NULL) {
        return -RT_EINVAL;
    }
    if (pos + size > dev->buffer_size) {
        return -RT_EFULL;
    }
    if (dev->read) {
        return dev->read(dev, pos, buffer, size);
    }
    return -RT_ERROR;
}

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• Local access to a system running RT-Thread <= 5.1.0.
• Ability to execute code (e.g., through a shell or a malicious application).
• Knowledge of the target device's memory layout.

Exploitation Steps:

1. Identify Vulnerable Functions: Use a disassembler or debugger to locate the sys_device_* functions in the RT-Thread kernel.
2. Craft Malicious Input: Prepare a payload that triggers the memory corruption. For example, if it's a buffer overflow, provide an oversized buffer to sys_device_write.
3. Trigger the Vulnerability: Call the vulnerable function with the crafted input.
4. Gain Control: Overwrite a function pointer or return address to redirect execution to shellcode.
5. Escalate Privileges: If successful, the shellcode runs in kernel mode, allowing full system control.

Example exploit code (conceptual):

// Conceptual exploit for buffer overflow in sys_device_write
#include <rtthread.h>

void exploit() {
    rt_device_t dev = rt_device_find("vuln_dev");
    if (dev) {
        char payload[1024];
        // Fill with shellcode and padding
        memset(payload, 0x90, sizeof(payload));
        // Overwrite return address
        *(uint32_t *)(payload + 100) = (uint32_t)shellcode;
        rt_device_write(dev, 0, payload, sizeof(payload));
    }
}

Blue Team (Defense)

Detection:

• Monitor for unusual system calls to device functions.
• Use kernel-level auditing to log all sys_device_* calls.
• Implement integrity checks on kernel memory.

Mitigation:

• Disable unused device drivers.
• Apply strict access controls to device files (e.g., /dev/).
• Use a kernel module to intercept and validate device operations.
• If possible, apply a memory protection mechanism like SMEP/SMAP.

Lab Setup:

• Use QEMU to emulate an RT-Thread system.
• Compile RT-Thread with debug symbols.
• Use GDB to step through the vulnerable functions.
• Test exploits in a sandboxed environment.

Indicators of Compromise (IOCs)

• File Hashes (SHA-256): (None available, but monitor for modified kernel modules)
• Process Names: Unusual processes calling sys_device_* functions.
• Network Connections: Unexpected outbound connections from embedded devices.
• System Logs: Kernel panics, memory corruption errors, or device driver crashes.
• Memory Patterns: Overwritten function pointers or return addresses in kernel memory.

Detection Engineering

YARA Rule

rule CVE_2025_6693_Memory_Corruption {
    meta:
        description = "Detects potential exploitation of CVE-2025-6693 in RT-Thread device driver"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-6693"
    strings:
        $s1 = "sys_device_open" ascii wide nocase
        $s2 = "sys_device_read" ascii wide nocase
        $s3 = "sys_device_write" ascii wide nocase
        $s4 = "sys_device_control" ascii wide nocase
        $s5 = "sys_device_init" ascii wide nocase
        $s6 = "sys_device_close" ascii wide nocase
        $s7 = "components/drivers/core/device.c" ascii wide nocase
    condition:
        any of ($s1, $s2, $s3, $s4, $s5, $s6) and $s7
}

Sigma Rule

title: CVE-2025-6693 RT-Thread Device Driver Memory Corruption
id: 8a4b3c2d-1e5f-4a7b-9c8d-0e1f2a3b4c5d
status: experimental
description: Detects exploitation attempts of CVE-2025-6693 via abnormal device driver calls
author: Valters IT
date: 2025/04/10
references:
    - https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2025-6693
logsource:
    category: process_creation
    product: linux
detection:
    selection:
        Image|endswith: '/rtthread'
        CommandLine|contains:
            - 'sys_device_open'
            - 'sys_device_read'
            - 'sys_device_write'
            - 'sys_device_control'
            - 'sys_device_init'
            - 'sys_device_close'
    condition: selection
falsepositives:
    - Legitimate RT-Thread system operations
level: high

Suricata Rule

alert ip any any -> any any (msg:"CVE-2025-6693 RT-Thread Device Driver Exploitation Attempt"; content:"|73 79 73 5f 64 65 76 69 63 65 5f|"; offset:0; depth:100; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Isolate Affected Systems: Disconnect RT-Thread devices from untrusted networks.
2. Restrict Local Access: Implement strict user authentication and authorization.
3. Monitor for Exploitation: Deploy the provided detection rules.

Long-Term Fixes:

• Vendor Patch: Await an official patch from RT-Thread. Since the vendor did not respond, consider forking the repository and applying a custom fix.
• Code Review: Manually audit the device.c file and apply bounds checking and input validation.
• Alternative OS: If possible, migrate to a more actively maintained RTOS.

Workarounds:

• Disable Vulnerable Functions: If not needed, remove or stub out the sys_device_* functions.
• Use a Kernel Module: Implement a security module that intercepts and validates device calls.
• Memory Protection: Enable hardware-based memory protection (e.g., MPU on ARM Cortex-M).

Valters IT