CVE-2025-43966

Executive Summary

CVE-2025-43966 is a low-severity vulnerability in the libheif library, affecting versions prior to 1.19.6. The vulnerability is a NULL pointer dereference in the ImageItem_iden function within image-items/iden.cc. This flaw can be triggered when processing a specially crafted HEIF/HEIC image file, leading to a denial of service (application crash). The CVSS score is 2.9, indicating a low threat level due to the requirement for user interaction and the limited impact (availability only). No public proof-of-concept (PoC) exploits or active exploitation have been reported as of this analysis.

Supply Chain & Package Security

libheif is a widely used open-source library for handling HEIF/HEIC image formats. It is a dependency for many image processing applications, including those in the Linux ecosystem (e.g., GIMP, ImageMagick, and various media players). A denial-of-service vulnerability in libheif can cascade to any application that uses it to parse untrusted HEIF files. While the immediate impact is limited to crashes, it highlights the importance of supply chain security and keeping dependencies updated.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:L
• Base Score: 2.9 (Low)
• Attack Vector (AV): Local (AV:L) – The attacker must have local access to the system or be able to deliver the malicious file to the user.
• Attack Complexity (AC): Low (AC:L) – No special conditions are required to exploit.
• Privileges Required (PR): None (PR:N) – No authentication needed.
• User Interaction (UI): Required (UI:R) – The victim must open the malicious file.
• Scope (S): Unchanged (S:U) – The vulnerability does not affect other components.
• Confidentiality (C): None (C:N) – No data exposure.
• Integrity (I): None (I:N) – No data modification.
• Availability (A): Low (A:L) – The application crashes, causing a denial of service.

Threat Level: Low. Exploitation requires user interaction and only results in a crash. No remote code execution or data theft is possible.

Deep Dive & Mechanics

The vulnerability resides in the ImageItem_iden function within the image-items/iden.cc file. This function is responsible for identifying image items within a HEIF file. A NULL pointer dereference occurs when the function attempts to access a pointer that has not been properly initialized or has been set to NULL due to malformed input.

Root Cause: The code does not properly validate the return value of a function call or the state of an object before dereferencing it. When a specially crafted HEIF file is processed, the function receives a NULL pointer where a valid object pointer is expected, leading to a crash.

Trigger: The vulnerability is triggered by opening a maliciously crafted HEIF/HEIC file. The file must contain specific structural anomalies that cause the ImageItem_iden function to encounter a NULL pointer.

Impact: The immediate impact is a denial of service (application crash). In a worst-case scenario, if the application is a critical service (e.g., a media server), repeated crashes could lead to service unavailability.

Vulnerable vs. Patched Code

Vulnerable Code (libheif < 1.19.6):

// image-items/iden.cc (simplified)
Error ImageItem_iden::parse(InputContext& input) {
    // ... some parsing logic ...
    auto* item = input.get_item(); // May return NULL for malformed input
    // VULNERABLE: No NULL check before dereference
    item->set_id(123); // NULL pointer dereference
    // ...
}

Patched Code (libheif >= 1.19.6):

// image-items/iden.cc (simplified)
Error ImageItem_iden::parse(InputContext& input) {
    // ... some parsing logic ...
    auto* item = input.get_item(); // May return NULL for malformed input
    // PATCH: Added NULL check
    if (item == nullptr) {
        return Error(heif_error_Invalid_input, heif_suberror_Unspecified);
    }
    item->set_id(123);
    // ...
}

The patch adds a NULL pointer check before dereferencing the item pointer. If the pointer is NULL, the function returns an error instead of crashing.

Exploitation & Lab Setup

Red Team (Offensive)

Prerequisites:

• A system with libheif < 1.19.6 installed.
• A tool to craft malicious HEIF files (e.g., a hex editor or a fuzzer like AFL++).

Steps:

1. Craft a Malicious HEIF File: Use a fuzzer or manually modify a valid HEIF file to introduce a NULL pointer condition in the ImageItem_iden parsing path. This typically involves corrupting the item reference table or the item identification box.
2. Deliver the File: Send the crafted file to the target via email, web download, or other means.
3. Trigger the Vulnerability: The victim opens the file with an application that uses libheif (e.g., an image viewer). The application crashes.

Example (Conceptual):

# Using a hex editor to corrupt a HEIF file
# This is a simplified example; actual exploitation requires deep knowledge of the HEIF format.
echo "Corrupted HEIF file" > malicious.heif
# The file would need specific byte modifications to trigger the NULL pointer.

Note: No public exploit code is available. This is a denial-of-service vulnerability only.

Blue Team (Defensive)

Detection:

• Monitor for application crashes related to libheif.
• Use file integrity monitoring to detect the presence of suspicious HEIF files.
• Implement network-level scanning for HEIF files (if applicable).

Prevention:

• Patch: Upgrade libheif to version 1.19.6 or later.
• Input Validation: Use a security-aware image processing pipeline that validates HEIF files before processing.
• Sandboxing: Run applications that process untrusted images in a sandboxed environment.

Hunting:

• Search for crash dumps or logs containing "ImageItem_iden" or "iden.cc".
• Look for unusual HEIF files in user upload directories or email attachments.

Indicators of Compromise (IOCs)

• File Hashes: No specific hashes available as no public PoC exists.
• File Names: *.heif, *.heic files with unusual sizes or structures.
• Log Entries:
  • Application crash logs referencing ImageItem_iden or iden.cc.
  • System logs showing segmentation faults in processes using libheif.
• Network Traffic: No specific network IOCs; the attack is file-based.

Detection Engineering

YARA Rule

rule CVE_2025_43966_libheif_NULL_deref {
    meta:
        description = "Detects HEIF files likely to trigger CVE-2025-43966 NULL pointer dereference"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-43966"
        hash = "unknown"
    strings:
        $heif_magic = { 00 00 00 18 66 74 79 70 6D 69 66 31 } // ftyp box for "mif1"
        $iden_box = { 69 64 65 6E } // "iden" box identifier
        $null_trigger = { 00 00 00 00 } // Potential NULL pointer trigger pattern
    condition:
        $heif_magic at 0 and $iden_box and #null_trigger > 3
}

Sigma Rule

title: CVE-2025-43966 libheif NULL Pointer Dereference
id: cve-2025-43966
status: experimental
description: Detects application crashes caused by CVE-2025-43966 in libheif
author: Valters IT
date: 2025-04-10
logsource:
    category: application
    product: linux
detection:
    selection:
        EventID: 11 # Example: Application crash event
        Image|endswith: '/libheif.so'
        TargetFilename|contains: 'iden.cc'
    condition: selection
falsepositives:
    - Legitimate crashes due to other bugs
level: low

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2025-43966 libheif HEIF File Download"; flow:to_server,established; content:"|00 00 00 18 66 74 79 70 6D 69 66 31|"; depth:12; content:".heif"; nocase; classtype:attempted-dos; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Patch: Upgrade libheif to version 1.19.6 or later. This is the only definitive fix.

   # For Debian/Ubuntu
   sudo apt-get update && sudo apt-get install libheif1
   # For RHEL/CentOS
   sudo yum update libheif
   # For source compilation
   wget https://github.com/strukturag/libheif/releases/download/v1.19.6/libheif-1.19.6.tar.gz
   tar -xzf libheif-1.19.6.tar.gz
   cd libheif-1.19.6
   ./configure && make && sudo make install
   

2. Workaround: If patching is not immediately possible, avoid processing untrusted HEIF files. Use alternative image formats (JPEG, PNG) where possible.
3. Monitor: Watch for any unusual application crashes and investigate.

Long-Term Mitigations:

• Implement a Web Application Firewall (WAF) to block HEIF file uploads if not needed.
• Use runtime protection tools (e.g., ASLR, NX) to mitigate the impact of crashes.
• Regularly update all dependencies, especially those handling untrusted input.

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