CVE-2025-6817

Executive Summary

CVE-2025-6817 is a locally exploitable resource consumption vulnerability in HDF5 version 1.14.6. The flaw resides in the H5C__load_entry function within /src/H5Centry.c, where improper handling of certain metadata entries can lead to uncontrolled resource consumption (CPU/memory exhaustion). The attack vector is local, requiring no authentication, and the exploit has been publicly disclosed. With a CVSS score of 3.3 (Low), the primary impact is denial of service (availability). No patch is currently available from the vendor.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
• Base Score: 3.3 (Low)
• 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: None (C:N)
• Integrity Impact: None (I:N)
• Availability Impact: Low (A:L) – Resource consumption leads to degraded performance or denial of service.

Threat Level: Low. The requirement for local access significantly reduces the attack surface. However, in shared environments or systems where untrusted users can execute code, this could be used to disrupt HDF5-based services.

Deep Dive & Mechanics

The vulnerability is located in the H5C__load_entry function, which is part of the HDF5 metadata cache. This function is responsible for loading metadata entries from disk into the cache. The flaw occurs when a specially crafted HDF5 file is opened, causing the function to enter an infinite loop or allocate excessive memory while processing a corrupted or malicious metadata entry.

Technical Details:

• The function H5C__load_entry in /src/H5Centry.c does not properly validate the size or structure of metadata entries before processing.
• By providing a file with a malformed entry (e.g., an entry with a zero-length or extremely large size field), the function may repeatedly attempt to read or allocate resources without bounds.
• This leads to CPU exhaustion (infinite loop) or memory exhaustion (unbounded allocation), resulting in a denial of service.

Attack Scenario:

1. An attacker crafts a malicious HDF5 file with a corrupted metadata entry.
2. The attacker places this file on a local filesystem accessible to the target system.
3. When a user or automated process opens the file using HDF5 library version 1.14.6, the vulnerability is triggered.
4. The system becomes unresponsive or crashes due to resource exhaustion.

Vulnerable vs. Patched Code

Since no patch is available, a direct code comparison cannot be provided. However, based on the vulnerability description, the following pseudo-code illustrates the likely vulnerable pattern and a potential fix:

Vulnerable Code (Conceptual):

// /src/H5Centry.c - H5C__load_entry (vulnerable)
herr_t H5C__load_entry(H5C_t *cache, haddr_t addr, const H5C_class_t *type) {
    // ... 
    size_t entry_size = read_entry_size_from_file(addr); // No validation
    H5C_cache_entry_t *entry = (H5C_cache_entry_t *)malloc(entry_size); // Potential overflow
    // ... loop reading data without bounds checking
    while (read_next_chunk(entry)) {
        // Process chunk - may never terminate if entry_size is 0 or malformed
    }
    // ...
}

Patched Code (Conceptual):

// /src/H5Centry.c - H5C__load_entry (patched)
herr_t H5C__load_entry(H5C_t *cache, haddr_t addr, const H5C_class_t *type) {
    // ...
    size_t entry_size = read_entry_size_from_file(addr);
    if (entry_size == 0 || entry_size > MAX_ENTRY_SIZE) {
        return FAIL; // Validate size
    }
    H5C_cache_entry_t *entry = (H5C_cache_entry_t *)malloc(entry_size);
    if (entry == NULL) {
        return FAIL; // Check allocation
    }
    size_t total_read = 0;
    while (total_read < entry_size) { // Bounded loop
        size_t chunk = read_next_chunk(entry, entry_size - total_read);
        if (chunk == 0) break; // Prevent infinite loop
        total_read += chunk;
    }
    // ...
}

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• Local access to a system running HDF5 1.14.6.
• Ability to write a malicious HDF5 file to the filesystem.

Exploit Steps:

1. Craft Malicious File: Use a hex editor or a custom script to create an HDF5 file with a corrupted metadata entry. The entry should have a size field set to 0 or a very large value.
2. Deliver File: Place the file in a location where it will be opened by an HDF5 application (e.g., /tmp/exploit.h5).
3. Trigger: Execute any HDF5 tool (e.g., h5dump, h5ls) on the malicious file:

   h5dump /tmp/exploit.h5
   

4. Observe: The application will hang or consume excessive CPU/memory, leading to denial of service.

Example Malicious File Generation (Python):

import struct

def create_malicious_hdf5(filename):
    # Minimal HDF5 superblock with corrupted metadata entry
    # This is a simplified example; real exploit requires deep HDF5 format knowledge
    with open(filename, 'wb') as f:
        # Superblock signature
        f.write(b'\x89HDF\r\n\x1a\n')
        # ... (other fields)
        # Corrupted entry: size = 0xFFFFFFFF (max uint32)
        f.write(struct.pack('<I', 0xFFFFFFFF))
        # ... (rest of file)

create_malicious_hdf5('exploit.h5')

Blue Team (Detection & Defense)

Detection:

• Monitor for HDF5 processes (e.g., h5dump, h5ls) that consume excessive CPU or memory.
• Use file integrity monitoring to detect creation of suspicious HDF5 files in sensitive directories.
• Enable logging of file open operations for HDF5 libraries.

Defense:

• Restrict local access to trusted users only.
• Use sandboxing or containerization to isolate HDF5 processing.
• Implement resource limits (ulimit) for HDF5 processes:

  ulimit -v 1048576  # Limit virtual memory to 1GB
  ulimit -t 30       # Limit CPU time to 30 seconds
  

• Validate HDF5 files before processing using a separate tool or library.

Indicators of Compromise (IOCs)

• File Hashes (Malicious HDF5):
  • SHA256: e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855 (example, replace with actual)
• Process Anomalies:
  • HDF5 processes (h5dump, h5ls, h5import) consuming >90% CPU for extended periods.
  • HDF5 processes allocating >1GB of memory.
• Network Indicators: None (local vulnerability).
• File System Indicators:
  • Unexpected .h5 files in /tmp/ or user home directories.
  • Files with unusual sizes (e.g., very small or very large) that trigger crashes.

Detection Engineering

YARA Rule

rule CVE_2025_6817_HDF5_Malicious_Entry {
    meta:
        description = "Detects malicious HDF5 files exploiting CVE-2025-6817"
        author = "Valters IT"
        date = "2025-04-10"
        hash = "unknown"
    strings:
        $hdf5_sig = { 89 48 44 46 0D 0A 1A 0A }
        $corrupt_size = { FF FF FF FF }  // 0xFFFFFFFF size field
    condition:
        $hdf5_sig at 0 and $corrupt_size in (8..1024)
}

Sigma Rule

title: HDF5 Resource Consumption Exploit Attempt
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects potential exploitation of CVE-2025-6817 via abnormal HDF5 process behavior
author: Valters IT
date: 2025-04-10
logsource:
    category: process_creation
    product: linux
detection:
    selection:
        Image|endswith:
            - '/h5dump'
            - '/h5ls'
            - '/h5import'
        CommandLine|contains: '.h5'
    condition: selection
    timeframe: 5m
    aggregation:
        - field: Image
          function: count
          condition: gt 10
falsepositives:
    - Legitimate large HDF5 file processing
level: medium

Suricata Rule

alert tcp any any -> any any (msg:"CVE-2025-6817 HDF5 Malicious File Transfer"; flow:to_client; fileext:"h5"; content:"|89 48 44 46 0D 0A 1A 0A|"; offset:0; depth:8; content:"|FF FF FF FF|"; within:1024; classtype:attempted-dos; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Restrict Access: Limit local user access to systems running HDF5 1.14.6.
2. Monitor: Implement the detection rules above to identify exploitation attempts.
3. Resource Limits: Apply system-level resource limits (ulimit) to HDF5 processes.

Long-term Fix:

• Vendor Patch: Await an official patch from the HDF5 group. Monitor HDF5 GitHub for updates.
• Workaround: If possible, avoid opening untrusted HDF5 files. Use a file validation tool before processing.
• Upgrade: When a patched version is released (e.g., 1.14.7 or later), upgrade immediately.

Valters IT
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