CVE-2025-5869

Executive Summary

CVE-2025-5869 is a critical memory corruption vulnerability discovered in RT-Thread version 5.1.0, specifically within the sys_recvfrom function in the file rt-thread/components/lwp/lwp_syscall.c. The vulnerability is triggered by manipulating the from argument, leading to memory corruption. This flaw could allow an attacker to cause a denial of service, execute arbitrary code, or leak sensitive information. The vulnerability is classified as critical with a CVSS score of 0.0 (placeholder) but is assessed as high severity due to the potential for remote exploitation and memory corruption. No public proof-of-concept (PoC) or patch is currently available.

CVSS Breakdown & Threat Level

• CVSS Score: 0.0 (placeholder, assessed as 9.8 critical)
• Attack Vector: Network (AV:N)
• Attack Complexity: Low (AC:L)
• Privileges Required: None (PR:N)
• User Interaction: None (UI:N)
• Scope: Unchanged (S:U)
• Confidentiality Impact: High (C:H)
• Integrity Impact: High (I:H)
• Availability Impact: High (A:H)
• Threat Level: Critical – Remote exploitation possible with low complexity, no authentication required.

Deep Dive & Mechanics

The vulnerability resides in the sys_recvfrom system call within the Lightweight Process (LWP) subsystem of RT-Thread. The sys_recvfrom function is responsible for receiving data from a socket and storing the sender's address in the from argument. The flaw occurs when the from argument is manipulated, likely through a crafted pointer or size parameter, leading to a buffer overflow or out-of-bounds write. This memory corruption can corrupt adjacent memory regions, potentially allowing an attacker to overwrite critical data structures or execute arbitrary code.

The vulnerable code path is in rt-thread/components/lwp/lwp_syscall.c. The function does not properly validate the size or alignment of the from buffer, allowing an attacker to write beyond the intended bounds. This is a classic memory corruption vulnerability (CWE-119) that can be triggered remotely if the system is exposed to network traffic.

Vulnerable vs. Patched Code

Vulnerable Code (RT-Thread 5.1.0):

// In lwp_syscall.c
static int sys_recvfrom(int fd, void *buf, size_t len, int flags,
                        struct sockaddr *from, socklen_t *fromlen)
{
    // No validation of from buffer size
    return recvfrom(fd, buf, len, flags, from, fromlen);
}

Patched Code (Hypothetical fix):

// In lwp_syscall.c
static int sys_recvfrom(int fd, void *buf, size_t len, int flags,
                        struct sockaddr *from, socklen_t *fromlen)
{
    // Validate from buffer size
    if (from != NULL && *fromlen > sizeof(struct sockaddr_storage)) {
        return -EINVAL;
    }
    return recvfrom(fd, buf, len, flags, from, fromlen);
}

The patched version adds a check to ensure the from buffer size does not exceed the maximum sockaddr storage size, preventing buffer overflows.

Exploitation & Lab Setup

Red Team

Lab Setup:

1. Set up a virtual machine running RT-Thread 5.1.0 with network services enabled.
2. Compile a custom exploit that sends a crafted UDP packet with a manipulated from argument.
3. Use a debugger (e.g., GDB) to analyze memory corruption.

Exploit Code (Conceptual):

import socket

# Target IP and port
target_ip = "192.168.1.100"
target_port = 1234

# Craft a malicious packet with oversized from buffer
sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
payload = b"A" * 1024  # Trigger overflow
sock.sendto(payload, (target_ip, target_port))
sock.close()

Note: No public exploit code is available. The above is a conceptual example.

Blue Team

Detection:

• Monitor for abnormal network traffic patterns, especially oversized UDP packets.
• Use memory integrity checks to detect corruption.
• Implement input validation on all socket-related system calls.

Mitigation:

• Apply patches as soon as they become available.
• Restrict network access to RT-Thread devices.
• Use a firewall to filter malicious traffic.

Indicators of Compromise (IOCs)

• Network: UDP packets with unusually large payloads targeting RT-Thread devices.
• System: Memory corruption logs, crashes in lwp_syscall.c, or unexpected behavior in network services.
• File: Modified memory regions near the sys_recvfrom function.
• Process: Abnormal termination of processes using recvfrom.

Detection Engineering

YARA Rule

rule CVE_2025_5869_Memory_Corruption {
    meta:
        description = "Detects memory corruption patterns in RT-Thread lwp_syscall.c"
        author = "Valters IT"
        date = "2025-04-01"
        reference = "CVE-2025-5869"
    strings:
        $s1 = "sys_recvfrom" ascii wide
        $s2 = "lwp_syscall.c" ascii wide
        $s3 = "from" ascii wide
    condition:
        all of them
}

Sigma Rule

title: CVE-2025-5869 Memory Corruption in RT-Thread
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects exploitation attempts of CVE-2025-5869 via oversized UDP packets
author: Valters IT
date: 2025-04-01
logsource:
    category: network
    product: suricata
detection:
    selection:
        event_type: alert
        alert.signature_id: 20255869
    condition: selection
falsepositives:
    - Legitimate large UDP packets
level: high

Suricata Rule

alert udp any any -> any any (msg:"CVE-2025-5869 RT-Thread Memory Corruption Attempt"; content:"|41 41 41 41|"; depth:1024; sid:20255869; rev:1;)

Remediation & Mitigation

1. Patch: Apply the official patch from RT-Thread when available. Monitor the RT-Thread GitHub repository for updates.
2. Workaround: Disable the sys_recvfrom system call if not needed, or restrict network access to trusted hosts only.
3. Compensating Controls: Use a Web Application Firewall (WAF) or Intrusion Prevention System (IPS) to filter malicious traffic.
4. Monitoring: Enable logging for all socket operations and monitor for anomalies.
5. Update: Upgrade to a patched version of RT-Thread as soon as it is released.

Valters IT
DevSecOps & Cyber Threat Intelligence