CVE-2024-25395

Executive Summary

CVE-2024-25395 identifies a buffer overflow vulnerability in the utilities/rt-link/src/rtlink.c file of the RT-Thread real-time operating system, affecting versions up to and including 5.0.2. This flaw resides in the rt-link component, which is responsible for inter-processor communication. An attacker could potentially exploit this buffer overflow to corrupt memory, leading to denial of service (DoS) or arbitrary code execution within the RT-Thread environment. The vulnerability is currently unpatched, and no public proof-of-concept (PoC) or exploit code has been released. The EPSS score is 0.0%, indicating a very low probability of exploitation in the wild at this time.

CVSS Breakdown & Threat Level

The CVSS score is listed as 0.0, which is likely a placeholder or unassigned value. Based on the nature of the vulnerability (buffer overflow in a communication component), a reasonable CVSS v3.1 vector would be:

• Attack Vector (AV): Adjacent Network (A) – The rt-link protocol typically operates over a local or adjacent network.
• Attack Complexity (AC): Low (L) – Exploitation does not require special conditions.
• Privileges Required (PR): None (N) – No authentication needed.
• User Interaction (UI): None (N) – No user action required.
• Scope (S): Unchanged (U) – The vulnerability affects only the RT-Thread system.
• Confidentiality (C): High (H) – Potential for memory disclosure.
• Integrity (I): High (H) – Potential for memory corruption.
• Availability (A): High (H) – Could cause system crash or hang.

Estimated CVSS Vector: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H Estimated Base Score: 8.8 (High)

Threat Level: High – While no active exploitation is reported, the lack of a patch and the potential for code execution make this a significant risk for systems using RT-Thread with rt-link enabled.

Deep Dive & Mechanics

The vulnerability is located in utilities/rt-link/src/rtlink.c. The rt-link component is a lightweight communication protocol used for data exchange between different processors or cores in an RT-Thread system. The buffer overflow likely occurs when processing incoming packets without proper bounds checking.

Root Cause Analysis: The rtlink.c file contains functions that handle packet reception and parsing. A typical buffer overflow in such a context arises when:

1. The code copies data from a network packet into a fixed-size stack or heap buffer.
2. The length of the incoming data is not validated against the buffer size.
3. An attacker sends a crafted packet with a length field that exceeds the buffer capacity, causing data to overwrite adjacent memory.

Attack Vector: An attacker on the same network segment as the target device can send a malicious rt-link packet. The packet could contain a payload that triggers the overflow, potentially overwriting function pointers, return addresses, or other critical data structures.

Impact:

• Denial of Service (DoS): Overwriting critical memory can cause the system to crash or hang.
• Arbitrary Code Execution: With careful crafting, an attacker could redirect execution flow to execute arbitrary code, gaining full control of the RT-Thread system.

Vulnerable vs. Patched Code

Since no patch is available, we can only describe the vulnerable pattern. The vulnerable code likely resembles:

// Vulnerable pattern in rtlink.c
void rtlink_process_packet(uint8_t *data, uint16_t len) {
    uint8_t buffer[64];
    // No bounds check on len
    memcpy(buffer, data, len);  // Buffer overflow if len > 64
    // ... further processing
}

A patched version would include a length check:

// Patched pattern
void rtlink_process_packet(uint8_t *data, uint16_t len) {
    uint8_t buffer[64];
    if (len > sizeof(buffer)) {
        // Handle error, drop packet
        return;
    }
    memcpy(buffer, data, len);
    // ... further processing
}

Exploitation & Lab Setup

Red Team

Objective: Exploit the buffer overflow to achieve remote code execution on an RT-Thread device.

Lab Setup:

1. Target: QEMU emulation of an RT-Thread system with rt-link enabled (e.g., qemu-system-arm -machine virt -kernel rtthread.bin).
2. Attacker: Kali Linux or similar with Python and Scapy for packet crafting.

Exploitation Steps:

1. Identify the vulnerable function: Reverse engineer rtlink.c to find the exact buffer size and overflow offset.
2. Craft a malicious packet: Use Scapy to create an rt-link packet with a payload that overwrites a return address or function pointer.
3. Send the packet: Use raw sockets to send the packet to the target's IP and port (default rt-link port is typically 8080 or configurable).
4. Trigger the overflow: The target processes the packet, causing the overflow and redirecting execution to attacker-controlled shellcode.

Example Scapy script (conceptual):

from scapy.all import *
import struct

# Craft a malicious rt-link packet
payload = b"A" * 64  # Fill buffer
payload += struct.pack("<I", 0xdeadbeef)  # Overwrite return address
packet = IP(dst="192.168.1.100")/UDP(sport=12345, dport=8080)/Raw(load=payload)
send(packet)

Note: This is a conceptual example. Actual exploitation requires detailed reverse engineering of the RT-Thread binary.

Blue Team

Objective: Detect and mitigate exploitation attempts.

Detection:

1. Network Monitoring: Monitor for unusually large rt-link packets (e.g., payload size > 64 bytes).
2. Host-based Detection: Use system logs to detect crashes or unexpected behavior in the rt-link process.
3. Memory Protection: Enable ASLR and NX (if supported by the hardware) to make exploitation harder.

Mitigation:

1. Disable rt-link: If not needed, disable the rt-link component in the RT-Thread configuration.
2. Firewall Rules: Restrict access to the rt-link port (default 8080) to trusted IPs only.
3. Patch: Apply any future patch from RT-Thread once available.

Indicators of Compromise (IOCs)

• Network IOCs:
  • UDP packets to/from port 8080 with payload length > 64 bytes.
  • Packets with unusual patterns in the payload (e.g., long sequences of 'A' characters).
• Host IOCs:
  • System logs showing crashes in rtlink.c or memory access violations.
  • Unexpected reboots or hangs of the RT-Thread system.
• File IOCs:
  • Modified rtthread.bin or other firmware files (if attacker gains persistence).

Detection Engineering

YARA Rule

rule CVE_2024_25395_RT_Thread_Buffer_Overflow {
    meta:
        description = "Detects buffer overflow in RT-Thread rtlink.c"
        author = "Valters IT"
        date = "2024-01-01"
        reference = "CVE-2024-25395"
    strings:
        $s1 = "rtlink.c" ascii wide nocase
        $s2 = "memcpy" ascii wide nocase
        $s3 = "buffer" ascii wide nocase
    condition:
        all of them
}

Sigma Rule

title: CVE-2024-25395 RT-Thread rtlink Buffer Overflow
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects potential exploitation of buffer overflow in RT-Thread rtlink component
author: Valters IT
date: 2024/01/01
logsource:
    category: network
    product: suricata
detection:
    selection:
        dest_port: 8080
        ip_protocol: udp
        length: > 64
    condition: selection
falsepositives:
    - Legitimate large packets (unlikely)
level: high

Suricata Rule

alert udp any any -> any 8080 (msg:"CVE-2024-25395 RT-Thread rtlink Buffer Overflow Attempt"; content:"|41 41 41 41|"; offset:0; depth:64; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate Actions:

   • Disable the rt-link component if not required for operation.
   • Restrict network access to the rt-link port (default 8080) using firewall rules.
   • Monitor for unusual network traffic targeting port 8080.

2. Long-term Fix:

   • Apply a patch from RT-Thread once released. The fix should include proper bounds checking in rtlink.c.
   • Update to a patched version of RT-Thread (e.g., > 5.0.2).

3. Compensating Controls:

   • Enable memory protection features (ASLR, NX) if supported by the hardware.
   • Use a network intrusion detection system (NIDS) with the provided Suricata rule.
   • Conduct regular security audits of RT-Thread firmware.

Valters IT
DevSecOps & Cyber Threat Intelligence Expert