CVE-2025-6269

Executive Summary

CVE-2025-6269 is a critical heap-based buffer overflow vulnerability in the HDF5 library, up to version 1.14.6. The flaw resides in the H5C__reconstruct_cache_entry function within H5Cimage.c. Successful exploitation requires local access and can lead to memory corruption, potentially enabling arbitrary code execution or denial of service. The vulnerability has been publicly disclosed, increasing the risk of exploitation. As of this report, no official patch is available, and the EPSS score is 0.0%, indicating low immediate exploitation activity.

Supply Chain & Package Security

This vulnerability affects the HDF5 library, a widely used data format for scientific and engineering applications. It is distributed as source code and pre-built binaries for various platforms. Organizations using HDF5 in their software supply chain should assess their exposure and consider temporary mitigations until a patch is released.

CVSS Breakdown & Threat Level

• CVSS Score: 5.3 (Medium)
• Attack Vector: Local (AV:L)
• Attack Complexity: Low (AC:L)
• Privileges Required: None (PR:N)
• User Interaction: None (UI:N)
• Scope: Unchanged (S:U)
• Confidentiality Impact: Low (C:L)
• Integrity Impact: Low (I:L)
• Availability Impact: Low (A:L)

The medium severity rating reflects the requirement for local access, but the low attack complexity and lack of privileges needed make it a viable threat in multi-user environments or where untrusted HDF5 files are processed.

Deep Dive & Mechanics

The vulnerability is a heap-based buffer overflow in the H5C__reconstruct_cache_entry function. This function is responsible for reconstructing a cache entry from a serialized image. The overflow occurs due to insufficient bounds checking when copying data into a heap buffer. An attacker can craft a malicious HDF5 file that, when opened and processed, triggers the overflow, potentially overwriting adjacent heap memory.

The root cause is likely an integer overflow or missing length validation in the reconstruction logic. The function reads a size field from the input and uses it to allocate or copy data without verifying that the size does not exceed the allocated buffer.

Vulnerable vs. Patched Code

Since no official patch is available, a comparison cannot be made. However, the vulnerable code path is in H5Cimage.c within the H5C__reconstruct_cache_entry function. A hypothetical fix would involve adding bounds checks before memory copy operations, ensuring that the size read from the input does not exceed the allocated buffer length.

Exploitation & Lab Setup

Red Team

To exploit this vulnerability, an attacker would need to craft a malicious HDF5 file that triggers the overflow. The following steps outline a potential exploitation scenario:

1. Craft a Malicious HDF5 File: Create an HDF5 file with a corrupted cache image that specifies an oversized size field.
2. Deliver the File: Use social engineering or other means to get the target to open the file with an HDF5-aware application.
3. Trigger the Overflow: When the application processes the file, the H5C__reconstruct_cache_entry function will overflow the heap buffer.
4. Achieve Code Execution: Overwrite critical heap structures or function pointers to gain control of the execution flow.

Example PoC (Conceptual):

import h5py
import numpy as np

# Create a malicious HDF5 file
with h5py.File('malicious.h5', 'w') as f:
    # This is a simplified example; actual exploitation requires deep knowledge of HDF5 internals
    f.create_dataset('data', data=np.zeros((100, 100)))
    # Manipulate internal metadata to trigger the overflow

Blue Team

To detect and defend against this vulnerability:

1. Monitor for Suspicious HDF5 Files: Use file integrity monitoring to detect the creation of unusual HDF5 files.
2. Sandbox Processing: Process HDF5 files in isolated environments to limit the impact of exploitation.
3. Apply ASLR and DEP: Ensure that Address Space Layout Randomization (ASLR) and Data Execution Prevention (DEP) are enabled to mitigate exploitation.
4. Use Heap Hardening: Employ heap hardening techniques such as guard pages and heap metadata protection.

Indicators of Compromise (IOCs)

• File Hashes: (Example) malicious.h5 - SHA256: a1b2c3d4e5f6...
• Process Behavior: Unusual memory allocation patterns or crashes in applications using HDF5.
• Network Traffic: None (local exploitation).
• Registry/File System: Modified HDF5 library files or unexpected HDF5 files in sensitive directories.

Detection Engineering

YARA Rule

rule CVE_2025_6269_HDF5_Overflow {
    meta:
        description = "Detects malicious HDF5 files exploiting CVE-2025-6269"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-6269"
    strings:
        $hdf5_magic = { 89 48 44 46 0D 0A 1A 0A } // HDF5 magic bytes
        $overflow_pattern = { FF FF FF FF } // Example oversized size field
    condition:
        $hdf5_magic at 0 and $overflow_pattern
}

Sigma Rule

title: CVE-2025-6269 HDF5 Heap Overflow Detection
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects potential exploitation of CVE-2025-6269 via process crashes or memory errors
author: Valters IT
date: 2025-04-10
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        Image|endswith: '\hdf5.dll'
        CommandLine|contains: '*.h5'
    condition: selection
falsepositives:
    - Legitimate HDF5 file processing
level: medium

Suricata Rule

alert tcp any any -> any any (msg:"CVE-2025-6269 HDF5 Heap Overflow Attempt"; flow:to_server; content:"|89 48 44 46 0D 0A 1A 0A|"; depth:8; content:"|FF FF FF FF|"; within:100; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

1. Apply Patches: Monitor the HDF5 project for an official patch and apply it as soon as it becomes available.
2. Restrict Access: Limit local access to systems processing HDF5 files to trusted users only.
3. Input Validation: Implement additional input validation for HDF5 files before processing.
4. Use Memory Safe Languages: Consider using memory-safe languages or libraries for processing untrusted data.
5. Monitor for Exploitation: Deploy detection rules (YARA, Sigma, Suricata) to identify exploitation attempts.

Valters IT
DevSecOps & Cyber Threat Intelligence