CVE-2025-2924

Executive Summary

CVE-2025-2924 is a heap-based buffer overflow vulnerability in the HDF5 library, affecting versions up to and including 1.14.6. The flaw resides in the H5HL__fl_deserialize function within src/H5HLcache.c, where improper validation of the free_block argument can lead to a heap buffer overflow. This vulnerability is classified as problematic with a CVSS score of 3.3, indicating low severity. The attack vector is local, requiring an attacker to have local access to the system. The exploit has been publicly disclosed, increasing the risk of targeted attacks. No official patch is currently available, and the EPSS score is 0.0%, suggesting low exploitation likelihood in the wild.

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. This vulnerability could impact downstream applications that rely on HDF5 for data serialization, potentially leading to denial of service or memory corruption. 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 Vector: CVSS:3.1/AV:L/AC:L/PR:L/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 required.
• Privileges Required: Low (PR:L) – The attacker needs basic user privileges.
• User Interaction: None (UI:N) – No user action needed.
• Scope: Unchanged (S:U) – The vulnerability does not affect other components.
• Confidentiality Impact: None (C:N) – No data exposure.
• Integrity Impact: None (I:N) – No data modification.
• Availability Impact: Low (A:L) – Potential for denial of service or memory corruption.

Threat Level: Low. The local attack vector and low impact reduce the immediate threat, but public exploit code increases risk for targeted attacks.

Deep Dive & Mechanics

The vulnerability is located in the H5HL__fl_deserialize function, which is part of the HDF5 library's cache layer. This function is responsible for deserializing free-list blocks from the HDF5 file format. The free_block argument, which represents a pointer to a free block in the heap, is manipulated without proper bounds checking. This can lead to a heap-based buffer overflow when the function writes data beyond the allocated buffer.

Root Cause: Insufficient validation of the free_block argument allows an attacker to craft a malicious HDF5 file that, when parsed, triggers a heap overflow. The overflow can corrupt adjacent heap metadata, potentially leading to a crash or arbitrary code execution under specific conditions.

Attack Scenario: An attacker with local access to the system can create a specially crafted HDF5 file. When a victim application (e.g., a data analysis tool) opens this file using the vulnerable HDF5 library, the overflow occurs. The attacker may exploit this to cause a denial of service or, in more complex scenarios, achieve code execution.

Vulnerable vs. Patched Code

Since no official patch is available, the vulnerable code path is identified in the H5HL__fl_deserialize function. The following is a conceptual comparison:

Vulnerable Code (HDF5 <= 1.14.6):

// src/H5HLcache.c
herr_t H5HL__fl_deserialize(H5HL_t *heap, const uint8_t *buf, size_t buf_size) {
    // ... 
    H5HL_free_t *free_block = (H5HL_free_t *)buf;
    // No bounds check on free_block->size or free_block->offset
    // ...
    // Potential overflow when copying data
    memcpy(heap->free_block, free_block, sizeof(H5HL_free_t));
    // ...
}

Patched Code (Hypothetical):

// src/H5HLcache.c
herr_t H5HL__fl_deserialize(H5HL_t *heap, const uint8_t *buf, size_t buf_size) {
    // ...
    if (buf_size < sizeof(H5HL_free_t)) {
        // Error handling
        return FAIL;
    }
    H5HL_free_t *free_block = (H5HL_free_t *)buf;
    // Validate free_block->size and offset
    if (free_block->size > heap->size || free_block->offset > heap->size) {
        return FAIL;
    }
    // Safe copy
    memcpy(heap->free_block, free_block, sizeof(H5HL_free_t));
    // ...
}

The patched version would include bounds checking on the free_block data before copying, preventing the overflow.

Exploitation & Lab Setup

Red Team

Exploitation Steps:

1. Craft Malicious HDF5 File: Create an HDF5 file with a corrupted free-list block that triggers the overflow. The exploit code is publicly available but not provided here.
2. Deliver File: Place the file on the target system via local access (e.g., USB, network share).
3. Trigger Vulnerability: Open the file using a vulnerable application (e.g., HDF5 viewer, data processing script).
4. Achieve Impact: The overflow can cause a crash (denial of service) or, with heap manipulation, potentially lead to code execution.

Lab Setup:

• Environment: Ubuntu 22.04 LTS with HDF5 1.14.6 installed.
• Tools: Python with h5py library, GDB for debugging.
• Proof of Concept: Use the public exploit to generate a malicious file and test locally.

Blue Team

Detection & Response:

• Monitor File Access: Log and alert on unusual HDF5 file access patterns, especially from untrusted sources.
• Memory Protection: Enable ASLR, DEP, and stack canaries to mitigate exploitation.
• Application Sandboxing: Run HDF5-consuming applications in sandboxed environments.
• User Education: Train users to avoid opening HDF5 files from untrusted sources.

Indicators of Compromise (IOCs)

• File Hashes: (SHA256 of malicious HDF5 file) – Not available publicly.
• Process Behavior: HDF5 library crashes or abnormal memory access patterns.
• Network Traffic: None (local attack).
• Log Entries: Application crash logs with references to H5HL__fl_deserialize or heap corruption.

Detection Engineering

YARA Rule

rule CVE_2025_2924_HDF5_HeapOverflow {
    meta:
        description = "Detects malicious HDF5 files exploiting CVE-2025-2924"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-2924"
    strings:
        $hdf5_magic = { 89 48 44 46 0D 0A 1A 0A } // HDF5 magic bytes
        $free_block_pattern = { FF FF FF FF } // Example pattern for corrupted free block
    condition:
        $hdf5_magic at 0 and $free_block_pattern
}

Sigma Rule

title: CVE-2025-2924 HDF5 Heap Overflow Detection
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects potential exploitation of CVE-2025-2924 via HDF5 file access
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: low

Suricata Rule

alert tcp any any -> any any (msg:"CVE-2025-2924 HDF5 Heap Overflow Attempt"; flow:to_server; content:"|89 48 44 46 0D 0A 1A 0A|"; depth:8; content:"|FF FF FF FF|"; within:1024; classtype:attempted-dos; sid:1000001; rev:1;)

Remediation & Mitigation

• Immediate: Disable automatic processing of HDF5 files from untrusted sources. Use file validation tools to check for malformed HDF5 structures.
• Short-term: Apply vendor patch when available. Monitor HDF5 security advisories.
• Long-term: Implement input validation and bounds checking in custom HDF5 parsers. Consider using memory-safe languages for critical components.
• Workaround: If patching is not possible, restrict local access to systems running HDF5 and monitor for abnormal crashes.

Valters IT