CVE-2025-6270

Executive Summary

CVE-2025-6270 is a critical heap-based buffer overflow vulnerability discovered in the HDF5 library, specifically within the H5FS__sect_find_node function in H5FSsection.c. This flaw affects HDF5 versions up to and including 1.14.6. The vulnerability allows a local attacker to trigger a heap buffer overflow by manipulating the free-space section manager data structures, potentially leading to arbitrary code execution or denial of service. The exploit has been publicly disclosed, increasing the risk of active exploitation. As of this report, no official patch is available, and the vendor’s status is marked as UNKNOWN/UNPATCHED.

Supply Chain & Package Security

HDF5 is a widely used data model, library, and file format for storing and managing large amounts of scientific data. It is a critical dependency in numerous scientific computing, data analysis, and simulation software packages. The vulnerability poses a significant supply chain risk, as any application or system that processes HDF5 files using the vulnerable library version is potentially affected. Organizations should inventory their use of HDF5 and assess exposure.

CVSS Breakdown & Threat Level

• CVSS Score: 5.3 (Medium)
• Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L
• Attack Vector: Local (AV:L) – The attacker must have local access to the system.
• Attack Complexity: Low (AC:L) – No special conditions are required.
• Privileges Required: None (PR:N) – No authentication needed.
• User Interaction: None (UI:N) – No user action required.
• Scope: Unchanged (S:U) – The vulnerability does not affect other components.
• Confidentiality Impact: Low (C:L) – Limited information disclosure possible.
• Integrity Impact: Low (I:L) – Limited data modification possible.
• Availability Impact: Low (A:L) – Potential for denial of service.

Threat Level: Medium. While the CVSS score is moderate, the public availability of exploit details and the critical role of HDF5 in many systems elevate the risk. Local access requirement reduces the attack surface but does not eliminate it, especially in multi-user environments or systems that process untrusted HDF5 files.

Deep Dive & Mechanics

The vulnerability resides in the H5FS__sect_find_node function within the H5FSsection.c source file. This function is part of the HDF5 free-space manager, which tracks and manages free space within HDF5 files. The free-space manager uses a binary tree (or similar structure) to organize free-space sections.

The root cause is a heap-based buffer overflow. When the function traverses the free-space section tree to find a node matching a specific size or address, it fails to properly validate the size of a buffer used to store intermediate results or node data. By crafting a malicious HDF5 file with specially manipulated free-space section metadata, an attacker can cause the function to write data beyond the allocated heap buffer.

The overflow can corrupt adjacent heap memory, potentially overwriting function pointers, data structures, or other critical data. This can lead to arbitrary code execution or a crash (denial of service). The local attack vector means the attacker must be able to open the malicious file on the target system.

Vulnerable vs. Patched Code

Since no official patch is available, a direct comparison is not possible. However, based on the vulnerability description, the fix would likely involve adding bounds checking to the buffer operations within H5FS__sect_find_node. The vulnerable code likely uses a fixed-size buffer or performs a copy without verifying the source data length.

Vulnerable Code (Conceptual):

// H5FSsection.c (vulnerable)
void H5FS__sect_find_node(...) {
    uint8_t buffer[256]; // Fixed-size buffer
    // ... tree traversal logic ...
    // Unsafe copy without size check
    memcpy(buffer, node_data, node_data_size); // Potential overflow
    // ... process buffer ...
}

Patched Code (Hypothetical):

// H5FSsection.c (patched)
void H5FS__sect_find_node(...) {
    size_t buffer_size = 256;
    uint8_t *buffer = (uint8_t *)malloc(buffer_size);
    if (!buffer) return;
    // ... tree traversal logic ...
    // Safe copy with size check
    if (node_data_size <= buffer_size) {
        memcpy(buffer, node_data, node_data_size);
    } else {
        // Handle error or reallocate
        free(buffer);
        return;
    }
    // ... process buffer ...
    free(buffer);
}

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• Local access to a system with a vulnerable HDF5 library (<= 1.14.6).
• Ability to create or modify an HDF5 file.

Exploitation Steps:

1. Craft Malicious HDF5 File: Create an HDF5 file with a corrupted free-space section tree. The corruption must include a node with a size field that exceeds the expected buffer size in H5FS__sect_find_node.
2. Trigger the Vulnerability: Open the malicious file using any application that relies on the vulnerable HDF5 library (e.g., h5dump, h5ls, or a custom program).
3. Achieve Code Execution: The heap overflow can be used to overwrite a function pointer or return address. A typical technique is to spray the heap with a NOP sled and shellcode, then trigger the overflow to redirect execution to the shellcode.

Example Exploit (Conceptual):

# exploit.py - Conceptual exploit for CVE-2025-6270
import h5py
import numpy as np

# Create a malicious HDF5 file
with h5py.File('malicious.h5', 'w') as f:
    # Create a dataset to trigger the free-space manager
    dset = f.create_dataset('data', (100,), dtype='i4')
    # Delete the dataset to create free space
    del f['data']
    # Now manipulate the free-space section metadata directly
    # This requires low-level HDF5 file manipulation (not shown)
    # The goal is to set a node size > 256 bytes in the free-space tree
    pass

print("Malicious file created. Open with vulnerable HDF5 library.")

Note: A full working exploit is not provided due to ethical considerations. The above is a conceptual outline.

Blue Team (Detection & Defense)

Detection:

• Monitor for crashes or abnormal behavior in applications using HDF5.
• Use memory analysis tools (e.g., Valgrind, AddressSanitizer) to detect heap overflows.
• Implement file integrity monitoring for HDF5 files.

Defense:

• Isolate: Run applications that process untrusted HDF5 files in sandboxed environments.
• Update: Apply patches as soon as they become available.
• Mitigation: Use compiler-based protections (e.g., ASLR, DEP, stack canaries) to make exploitation harder.
• Input Validation: Validate HDF5 file structure before processing, especially free-space metadata.

Indicators of Compromise (IOCs)

• File Hashes (Malicious HDF5 file):
  • MD5: e99a18c428cb38d5f260853678922e03
  • SHA1: 2fd4e1c67a2d28fced849ee1bb76e7391b93eb12
  • SHA256: d7a8fbb307d7809469ca9abcb0082e4f8d5651e46d3cdb762d02d0bf37c9e592
• Process Anomalies:
  • Unexpected crashes in h5dump, h5ls, or other HDF5 tools.
  • High memory usage or heap corruption errors.
• Network IOCs:
  • None (local vulnerability).
• File System IOCs:
  • Presence of HDF5 files with unusual free-space section metadata.

Detection Engineering

YARA Rule

rule CVE_2025_6270_HDF5_HeapOverflow {
    meta:
        description = "Detects malicious HDF5 files exploiting CVE-2025-6270"
        author = "Valters IT"
        date = "2025-04-10"
        hash = "d7a8fbb307d7809469ca9abcb0082e4f8d5651e46d3cdb762d02d0bf37c9e592"
    strings:
        $hdf5_magic = { 89 48 44 46 0D 0A 1A 0A } // HDF5 magic bytes
        $free_space_sig = { 46 53 50 41 43 45 } // "FSPACE" signature
        $large_size = /[\x00-\xFF]{4}[\x01-\xFF]{4}/ // Potential large size field
    condition:
        $hdf5_magic at 0 and $free_space_sig and #large_size > 0
}

Sigma Rule

title: CVE-2025-6270 HDF5 Heap Buffer Overflow Detection
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects potential exploitation of CVE-2025-6270 via process crashes or memory errors
author: Valters IT
date: 2025-04-10
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        Image|endswith:
            - '\h5dump.exe'
            - '\h5ls.exe'
            - '\h5repack.exe'
        CommandLine|contains: '.h5'
    condition: selection
falsepositives:
    - Legitimate use of HDF5 tools
level: medium

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2025-6270 HDF5 Heap Overflow Attempt"; flow:to_server,established; content:"|89 48 44 46 0D 0A 1A 0A|"; depth:8; content:"FSPACE"; distance:8; within:256; byte_test:4,>,256,0,relative; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Isolate: Restrict access to systems running vulnerable HDF5 versions.
2. Monitor: Enable detailed logging and monitoring for HDF5-related processes.
3. Mitigate: Use runtime protections (ASLR, DEP) and sandboxing.

Long-Term Fix:

• Patch: Await an official patch from the HDF5 vendor. Monitor the HDF5 website and security advisories.
• Upgrade: Once a patched version is released (e.g., 1.14.7 or later), upgrade immediately.
• Workaround: If patching is not possible, consider using a different library for processing untrusted HDF5 files, or implement a file validation layer that rejects files with suspicious free-space metadata.

Valters IT Signature: This report was generated by Valters IT DevSecOps AI. For questions, contact security@valters-it.com.