CVE-2025-2926

Executive Summary

CVE-2025-2926 is a locally exploitable null pointer dereference vulnerability in the HDF5 library, affecting versions up to and including 1.14.6. The flaw resides in the H5O__cache_chk_serialize function within src/H5Ocache.c. An attacker with local access can trigger a null pointer dereference, leading to a denial of service (DoS) condition. The vulnerability has a low CVSS score of 3.3 due to the requirement for local access and the limited impact (availability only). No patch is currently available from the vendor, and the exploit has been publicly disclosed.

Supply Chain & Package Security

This vulnerability affects the HDF5 library, which is a widely used data storage and management library in scientific computing, big data, and machine learning ecosystems. It is distributed as a source package and through package managers like Conda, vcpkg, and system package managers (e.g., apt, yum). Organizations using HDF5 in their software supply chain should assess their exposure and consider temporary mitigations until an official patch is released.

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 (AV): Local (L) – The attacker must have local access to the system.
• Attack Complexity (AC): Low (L) – No special conditions are required.
• Privileges Required (PR): None (N) – No privileges are needed to trigger the vulnerability.
• User Interaction (UI): None (N) – No user action is required.
• Scope (S): Unchanged (U) – The vulnerability does not affect other components.
• Confidentiality (C): None (N) – No data exposure.
• Integrity (I): None (N) – No data modification.
• Availability (A): Low (L) – The vulnerability can cause a denial of service.

Threat Level: Low. The requirement for local access significantly reduces the attack surface. However, in multi-tenant environments or systems where untrusted users can execute code, this could be leveraged for a DoS attack.

Deep Dive & Mechanics

The vulnerability is a null pointer dereference in the H5O__cache_chk_serialize function. This function is part of HDF5's metadata cache serialization logic. When the library attempts to serialize a cached object header (H5O), it may encounter a null pointer in a specific code path. The exact trigger condition involves crafting a specially malformed HDF5 file that, when opened and processed, causes the function to dereference a null pointer.

The affected code path is in src/H5Ocache.c. The function H5O__cache_chk_serialize is responsible for writing object header chunks to the metadata cache. A null pointer dereference occurs when a pointer to a data structure is not properly initialized or is set to NULL due to an error condition, and the code attempts to access its members without a null check.

Technical Details:

• The vulnerability is triggered by opening a maliciously crafted HDF5 file.
• The null pointer dereference leads to a segmentation fault, crashing the application.
• The attack is local, meaning the attacker must be able to execute code on the target system or trick a user into opening a malicious file.

Vulnerable vs. Patched Code

Since no official patch is available, the vulnerable code is identified as the H5O__cache_chk_serialize function in src/H5Ocache.c. The fix would involve adding a null pointer check before dereferencing the pointer.

Vulnerable Code (Conceptual):

// Vulnerable: No null check before dereference
void H5O__cache_chk_serialize(...) {
    some_struct *ptr = get_some_pointer(...);
    // ... some code ...
    if (some_condition) {
        // ptr could be NULL here
        ptr->field = value;  // Null pointer dereference
    }
}

Patched Code (Conceptual):

// Patched: Added null check
void H5O__cache_chk_serialize(...) {
    some_struct *ptr = get_some_pointer(...);
    // ... some code ...
    if (some_condition) {
        if (ptr == NULL) {
            // Handle error gracefully
            return;
        }
        ptr->field = value;  // Safe dereference
    }
}

Exploitation & Lab Setup

Red Team

Prerequisites:

• Local access to a system running an application that uses HDF5 library version <= 1.14.6.
• Ability to create or modify an HDF5 file.

Exploitation Steps:

1. Craft a malicious HDF5 file that triggers the null pointer dereference in H5O__cache_chk_serialize.
2. Deliver the file to the target system (e.g., via email, file upload, or shared drive).
3. When the target application opens the file, the vulnerability is triggered, causing a denial of service.

Proof-of-Concept (PoC) Code:

# PoC: Create a malformed HDF5 file to trigger CVE-2025-2926
import h5py
import numpy as np

# Create a valid HDF5 file first
with h5py.File('malicious.h5', 'w') as f:
    f.create_dataset('data', data=np.array([1,2,3]))

# Modify the file to trigger the vulnerability (conceptual)
# This would involve binary patching of the HDF5 file structure
# to cause a null pointer dereference in H5O__cache_chk_serialize.
# The exact binary manipulation is not publicly available.
print("PoC file created. Open with vulnerable HDF5 library to trigger DoS.")

Blue Team

Detection:

• Monitor for crashes or segmentation faults in applications using HDF5.
• Use file integrity monitoring to detect the creation of unusual HDF5 files.
• Implement application whitelisting to prevent untrusted applications from opening HDF5 files.

Mitigation:

• Restrict local access to systems running HDF5-based applications.
• Use sandboxing or containerization to isolate applications.
• Monitor for known exploit patterns in HDF5 file parsing.

Indicators of Compromise (IOCs)

• File Hashes: (No specific hashes available for exploit files)
• Process Behavior: Segmentation fault (SIGSEGV) in processes using libhdf5.
• Log Entries: Application crash logs indicating a null pointer dereference in H5O__cache_chk_serialize.
• Network: None (local vulnerability).
• File Artifacts: Malicious HDF5 files with corrupted object header metadata.

Detection Engineering

YARA Rule

rule CVE_2025_2926_HDF5_Null_Pointer {
    meta:
        description = "Detects HDF5 files potentially crafted to exploit CVE-2025-2926"
        author = "Valters IT"
        date = "2025-04-08"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2025-2926"
    strings:
        $hdf5_magic = { 89 48 44 46 0D 0A 1A 0A }  // HDF5 magic bytes
        $null_trigger = { 00 00 00 00 }  // Potential null pointer trigger pattern
    condition:
        $hdf5_magic at 0 and #null_trigger > 5
}

Sigma Rule

title: CVE-2025-2926 HDF5 Null Pointer Dereference
id: 8a4b3c2d-1e5f-4a7b-9c8d-0e1f2a3b4c5d
status: experimental
description: Detects crashes related to null pointer dereference in HDF5 library
author: Valters IT
date: 2025-04-08
logsource:
    product: linux
    service: syslog
detection:
    selection:
        - EventID: 11  # Generic crash event
        - Message: '*H5O__cache_chk_serialize*'
        - Message: '*null pointer*'
    condition: selection
falsepositives:
    - Legitimate HDF5 file parsing errors
level: medium

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2025-2926 HDF5 Null Pointer Exploit Attempt"; flow:to_server; content:"|89 48 44 46 0D 0A 1A 0A|"; depth:8; content:"|00 00 00 00|"; distance:0; within:1024; classtype:attempted-dos; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Isolate: Restrict local access to systems running HDF5-based applications.
2. Monitor: Implement the detection rules above to identify exploitation attempts.
3. Update: Watch for an official patch from the HDF5 project. Apply it as soon as it becomes available.

Long-Term Mitigation:

• Code Review: Review the H5O__cache_chk_serialize function and add null pointer checks.
• Static Analysis: Use static analysis tools to identify similar null pointer dereference vulnerabilities.
• Sandboxing: Run HDF5-based applications in sandboxed environments to limit the impact of a crash.

Workarounds:

• If possible, avoid processing untrusted HDF5 files.
• Use file validation tools to check HDF5 file integrity before opening.

Valters IT