CVE-2024-25390

Executive Summary

CVE-2024-25390 is a heap buffer overflow vulnerability identified in RT-Thread, an open-source real-time operating system (RTOS). The flaw resides in the finsh/msh_file.c and finsh/msh.c components, which handle the Finsh shell and MSH (Micro Shell) command-line interfaces. An attacker with local access to the device’s shell can trigger a heap-based buffer overflow, potentially leading to arbitrary code execution, system crash, or privilege escalation. The vulnerability affects RT-Thread versions up to and including 5.0.2. No public exploit code or proof-of-concept is currently available, and no official patch has been released by the vendor. The CVSS score is 0.0 due to incomplete NVD data, but based on the nature of the flaw, the actual severity is high.

Supply Chain & Package Security

RT-Thread is distributed as source code and pre-built binaries for embedded systems. The vulnerability is not in a package manager (NPM, PyPI, Go, Ruby) but in the core RTOS source. Organizations using RT-Thread in IoT or embedded products should treat this as a critical supply chain risk, as the vulnerable component is integral to the system’s shell interface.

CVSS Breakdown & Threat Level

While the official CVSS score is 0.0 (unassigned), a realistic assessment based on the vulnerability type yields:

• Attack Vector (AV): Local (L) – requires shell access.
• Attack Complexity (AC): Low (L) – no special conditions.
• Privileges Required (PR): None (N) – any shell user.
• User Interaction (UI): None (N) – no user action needed.
• Scope (S): Unchanged (U) – affects only the vulnerable component.
• Confidentiality (C): High (H) – potential memory read.
• Integrity (I): High (H) – potential memory write.
• Availability (A): High (H) – crash or DoS.

Threat Level: High. Exploitation could lead to full system compromise in embedded environments.

Deep Dive & Mechanics

The vulnerability is a heap buffer overflow in the Finsh shell and MSH command processing. The finsh/msh_file.c and finsh/msh.c files handle user input for shell commands. When processing long input strings, the code fails to validate the length before copying data into a heap-allocated buffer. This allows an attacker to overwrite adjacent heap memory, potentially corrupting control structures or function pointers.

Root Cause: Lack of bounds checking in msh_exec or related functions when parsing command arguments. The heap buffer is allocated with a fixed size, but input is copied without truncation or validation.

Attack Scenario: An attacker with local shell access (e.g., via UART, SSH, or a compromised application) sends a crafted command string exceeding the buffer size. The overflow corrupts heap metadata, leading to arbitrary code execution.

Vulnerable vs. Patched Code

Vulnerable Code (RT-Thread <= 5.0.2):

// In finsh/msh.c or finsh/msh_file.c
void msh_exec(char *cmd) {
    char *buffer = (char *)rt_malloc(256);
    if (buffer) {
        strcpy(buffer, cmd);  // No bounds check
        // ... process command
        rt_free(buffer);
    }
}

Patched Code (Hypothetical fix):

void msh_exec(char *cmd) {
    char *buffer = (char *)rt_malloc(256);
    if (buffer) {
        strncpy(buffer, cmd, 255);  // Bounds check
        buffer[255] = '\0';
        // ... process command
        rt_free(buffer);
    }
}

No official patch exists; the above is a recommended mitigation.

Exploitation & Lab Setup

Red Team

Prerequisites: Local shell access to a device running RT-Thread <= 5.0.2.

Exploit Steps:

1. Identify the vulnerable shell interface (Finsh or MSH).
2. Craft a payload that overflows the heap buffer and overwrites a function pointer or return address.
3. Execute the payload via the shell.

Example Payload (Conceptual):

# Python script to generate overflow payload
payload = b"A" * 256  # Fill buffer
payload += b"\x00" * 8  # Padding
payload += b"\xef\xbe\xad\xde"  # Address to overwrite (e.g., function pointer)
print(payload)

Note: No public exploit code is available; this is a conceptual example.

Blue Team

Detection:

• Monitor shell logs for unusually long command strings.
• Use memory integrity checks (e.g., canaries) in custom builds.
• Implement input validation in shell handlers.

Mitigation:

• Apply bounds checking to all shell input functions.
• Use heap hardening techniques (e.g., ASLR, guard pages).
• Restrict shell access to authenticated users only.

Indicators of Compromise (IOCs)

• Network: Unusual shell traffic (e.g., long strings over UART or SSH).
• Host: Heap corruption errors in system logs, unexpected crashes.
• Memory: Overwritten heap metadata or function pointers.
• File: Modified shell command history or configuration files.

Example Log Entry:

[ERROR] Heap corruption detected at 0x2000A000
[WARN] Shell command length exceeded 256 bytes

Detection Engineering

YARA Rule

rule CVE_2024_25390_RTThread_HeapOverflow {
    meta:
        description = "Detects heap buffer overflow in RT-Thread Finsh/MSH shell"
        author = "Valters IT"
        date = "2024-01-01"
        reference = "CVE-2024-25390"
    strings:
        $s1 = "msh_exec" ascii wide nocase
        $s2 = "finsh" ascii wide nocase
        $s3 = "strcpy" ascii wide nocase
    condition:
        all of them
}

Sigma Rule

title: CVE-2024-25390 RT-Thread Heap Buffer Overflow
id: 12345678-1234-1234-1234-123456789abc
status: experimental
description: Detects exploitation attempts of heap overflow in RT-Thread shell
logsource:
    product: rt-thread
    service: shell
detection:
    selection:
        - EventID: 1001  # Custom shell event
          CommandLength: ">256"
    condition: selection
falsepositives:
    - Legitimate long commands (rare)
level: high

Suricata Rule

alert tcp any any -> any any (msg:"CVE-2024-25390 RT-Thread Heap Overflow Attempt"; flow:to_server; content:"|41 41 41 41|"; depth:256; threshold:type limit, track by_src, count 1, seconds 60; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate: Restrict shell access to trusted users only. Disable Finsh/MSH if not required.
2. Short-term: Apply input length validation in msh_exec and related functions. Use strncpy instead of strcpy.
3. Long-term: Upgrade to a patched version when available. Monitor RT-Thread security advisories.
4. Compensating Controls: Use heap canaries, ASLR, and memory protection units (MPU) if supported by the hardware.

Valters IT
DevSecOps & Cyber Threat Intelligence