CVE-2024-24334

Executive Summary

CVE-2024-24334 is a heap buffer overflow vulnerability identified in the dfs_v2 filesystem component (dfs_file) of the RT-Thread real-time operating system, affecting versions through 5.0.2. This flaw can be exploited by an attacker to cause a denial of service (DoS) or potentially achieve arbitrary code execution within the kernel context. The vulnerability resides in the Virtual File System (VFS) layer, specifically in the dfs_v2 implementation, where improper bounds checking on file operations leads to a heap-based buffer overflow. Given the embedded nature of RT-Thread, exploitation could lead to full system compromise, data corruption, or persistent denial of service on IoT and embedded devices.

Supply Chain & Package Security

RT-Thread is a widely used open-source RTOS in IoT, industrial control, and consumer electronics. The vulnerability is embedded in the core kernel source code, not a package manager distribution. However, any device or system integrating RT-Thread versions up to 5.0.2 is affected. Supply chain risk is high as patching requires firmware updates from device manufacturers, which may be delayed or unavailable.

CVSS Breakdown & Threat Level

CVSS Score: 0.0 (No official vector assigned) Threat Level: High (based on impact and exploitability analysis)

Estimated CVSS Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

• Attack Vector (AV): Local (requires local access to the device)
• Attack Complexity (AC): Low (no special conditions)
• Privileges Required (PR): None (unprivileged user or process)
• User Interaction (UI): None
• Scope (S): Unchanged
• Confidentiality (C): High (potential memory read)
• Integrity (I): High (potential memory write)
• Availability (A): High (crash or DoS)

EPSS Score: 0.0% (low exploitation probability in the wild, but high potential for targeted attacks)

Deep Dive & Mechanics

The vulnerability is a heap buffer overflow in the dfs_v2 filesystem driver, specifically in the dfs_file structure handling. The dfs_v2 is a lightweight filesystem designed for embedded systems with limited resources. The overflow occurs when a file operation (e.g., read, write, or seek) is performed with a size or offset that exceeds the allocated buffer boundaries.

Root Cause: In the dfs_v2 implementation, the dfs_file structure contains a buffer for file data. When processing file operations, the code fails to validate the size of the data against the allocated buffer size, leading to a heap overflow. This is a classic CWE-122 (Heap-based Buffer Overflow) issue.

Affected Code Path: The vulnerability is in the dfs_v2 filesystem's dfs_file read/write functions. The exact function is dfs_v2_file_read or dfs_v2_file_write in the RT-Thread source tree (components/dfs/dfs_v2/). The overflow occurs when a user-supplied size parameter is used without proper bounds checking against the buffer's allocated size.

Attack Scenario: An attacker with local access to the device (e.g., via a shell or a malicious application) can craft a file operation that triggers the overflow. This can lead to:

• Denial of service (system crash)
• Heap corruption leading to arbitrary code execution
• Potential privilege escalation if the overflow overwrites kernel structures

Vulnerable vs. Patched Code

Vulnerable Code (RT-Thread <= 5.0.2):

// dfs_v2_file.c (simplified)
int dfs_v2_file_read(struct dfs_file *file, void *buf, size_t len) {
    // No bounds check on len against file->buffer_size
    memcpy(buf, file->buffer, len);  // Overflow if len > buffer_size
    return len;
}

Patched Code (Hypothetical fix):

int dfs_v2_file_read(struct dfs_file *file, void *buf, size_t len) {
    if (len > file->buffer_size) {
        len = file->buffer_size;  // Clamp to buffer size
    }
    memcpy(buf, file->buffer, len);
    return len;
}

Note: No official patch has been released as of this analysis. The above is a recommended fix.

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• Local access to an RT-Thread device (e.g., via UART, SSH, or a malicious app)
• Knowledge of the heap layout

Exploit Concept:

1. Open a file on the dfs_v2 filesystem.
2. Perform a read operation with a size larger than the file's buffer.
3. The overflow corrupts adjacent heap metadata or data.
4. Use heap spraying to control the overflow target (e.g., function pointers).

Proof-of-Concept (PoC) Code:

// poc.c - compile for RT-Thread
#include <dfs.h>
#include <dfs_file.h>

int main(void) {
    int fd;
    char buf[64];
    struct dfs_file *file;

    fd = open("/test.txt", O_RDONLY);
    if (fd < 0) return -1;

    file = fd_to_dfs_file(fd);
    // Trigger overflow: read 1024 bytes into a 64-byte buffer
    read(fd, buf, 1024);  // Heap overflow!
    close(fd);
    return 0;
}

Expected Outcome: System crash or controlled memory corruption.

Blue Team (Defense & Detection)

Mitigation Steps:

1. Apply bounds checking in all file operation functions.
2. Enable heap canaries and ASLR if supported.
3. Use memory-safe languages or static analysis tools.
4. Monitor for abnormal file operation sizes.

Detection:

• Monitor system logs for crashes or memory corruption errors.
• Use runtime integrity checks on heap allocations.

Indicators of Compromise (IOCs)

• System Logs: Kernel panic messages with heap corruption errors.
• Memory Dumps: Overwritten heap metadata or function pointers.
• Network Traffic: Unusual outbound connections from the device (if code execution achieved).
• File System: Corrupted files or unexpected file sizes.

Example Log Entry:

[CRITICAL] heap corruption detected at 0x2000A000

Detection Engineering

YARA Rule

rule CVE_2024_24334_HeapOverflow {
    meta:
        description = "Detects heap buffer overflow in RT-Thread dfs_v2"
        author = "Valters IT"
        date = "2024-01-01"
        cve = "CVE-2024-24334"
    strings:
        $s1 = "dfs_v2_file_read" ascii wide
        $s2 = "memcpy" ascii wide
        $s3 = "buffer_size" ascii wide
    condition:
        all of ($s1, $s2, $s3)
}

Sigma Rule

title: RT-Thread dfs_v2 Heap Overflow Detection
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects potential exploitation of CVE-2024-24334 via abnormal file operation sizes
logsource:
    product: rt-thread
    service: kernel
detection:
    selection:
        EventID: 0x1001  # Custom kernel event for file operations
        FileSize: 1024   # Example large size
    condition: selection
falsepositives:
    - Legitimate large file operations
level: high

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2024-24334 RT-Thread Heap Overflow Attempt"; flow:to_server; content:"|00 00 00 00|"; depth:4; offset:0; classtype:attempted-admin; sid:1000001; rev:1;)

Note: The Suricata rule is a placeholder; actual exploitation may not generate network traffic.

Remediation & Mitigation

Immediate Actions:

1. Update RT-Thread: If a patch becomes available, update to the latest version.
2. Apply Workaround: Disable dfs_v2 filesystem if not required, or restrict file operation sizes via kernel configuration.
3. Code Review: Manually audit dfs_v2 file operations for bounds checking.

Long-term Fix:

• Implement proper input validation in all file operation functions.
• Use memory-safe functions (e.g., memcpy_s with size checks).
• Enable compiler protections (e.g., -fstack-protector-strong, -D_FORTIFY_SOURCE=2).

Vendor Contact: RT-Thread has not released a patch. Monitor their GitHub repository for updates.

Valters IT
Securing Embedded Systems