CVE-2024-28564

Executive Summary

CVE-2024-28564 is a buffer overflow vulnerability in the open-source FreeImage library, version 3.19.0 [r1909]. The flaw resides in the Imf_2_2::CharPtrIO::readChars() function, which is invoked when processing images in the EXR (OpenEXR) format. A local attacker can exploit this vulnerability to cause a denial of service (DoS) by providing a specially crafted EXR image file. The vulnerability is classified as a classic buffer overflow (CWE-120), where improper bounds checking allows an attacker to write beyond the allocated buffer, potentially leading to application crashes or arbitrary code execution under certain conditions. As of the latest analysis, no official patch has been released, and no public proof-of-concept (PoC) code is available.

Supply Chain & Package Security

FreeImage is a widely used open-source library for image format handling, integrated into numerous applications and systems. This vulnerability poses a supply chain risk, as any software that statically or dynamically links to the vulnerable FreeImage version (3.19.0 [r1909]) is susceptible. Organizations should audit their dependencies for FreeImage usage and consider temporary mitigations until an official patch is released.

CVSS Breakdown & Threat Level

• CVSS Score: 0.0 (NVD assigned, likely due to incomplete data)
• CVSS Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
• Attack Vector (AV): Local (L) – The attacker must have local access to the system or be able to deliver the malicious file locally.
• Attack Complexity (AC): Low (L) – No special conditions are required to exploit.
• Privileges Required (PR): None (N) – No authentication needed.
• User Interaction (UI): Required (R) – The victim must open the malicious EXR file.
• 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): High (H) – Successful exploitation leads to a denial of service.

Threat Level: Medium (due to local attack vector and user interaction requirement, but high availability impact).

Deep Dive & Mechanics

The vulnerability is a buffer overflow in the Imf_2_2::CharPtrIO::readChars() function within FreeImage's EXR (OpenEXR) parser. The EXR format is a high-dynamic-range image format used in professional imaging and visual effects. The readChars() function is responsible for reading character data from the EXR file stream. Due to insufficient bounds checking, when processing a crafted EXR file, the function can write more data into a fixed-size buffer than it can hold, causing a buffer overflow.

Technical Details:

• The vulnerable function is part of the Imf_2_2 namespace, which corresponds to the OpenEXR library integration within FreeImage.
• The overflow occurs when the function attempts to read a large number of characters from the file without verifying that the destination buffer has sufficient capacity.
• This can lead to corruption of adjacent memory, potentially causing the application to crash (DoS) or, in more sophisticated attacks, allowing arbitrary code execution.

Attack Vector:

1. An attacker crafts a malicious EXR image file with specially crafted header or data fields that trigger the overflow.
2. The attacker delivers the file to the victim via email, download, or other means.
3. When the victim opens the file using an application that relies on the vulnerable FreeImage library, the overflow is triggered.

Vulnerable vs. Patched Code

Since no official patch is available, a direct comparison is not possible. However, based on the vulnerability description, the fix would involve adding proper bounds checking in the Imf_2_2::CharPtrIO::readChars() function.

Vulnerable Code (Conceptual):

void CharPtrIO::readChars(char* buffer, int count) {
    // No bounds checking on buffer size
    for (int i = 0; i < count; i++) {
        buffer[i] = readByte(); // Potential overflow if count > buffer size
    }
}

Patched Code (Conceptual):

void CharPtrIO::readChars(char* buffer, int bufferSize, int count) {
    // Bounds checking
    int safeCount = (count < bufferSize) ? count : bufferSize;
    for (int i = 0; i < safeCount; i++) {
        buffer[i] = readByte();
    }
}

Exploitation & Lab Setup

Red Team (Exploitation)

As no public exploit code is available, exploitation would require developing a custom proof-of-concept. The following steps outline a potential approach:

1. Environment Setup:

   • Install FreeImage 3.19.0 [r1909] on a test system (e.g., Ubuntu 22.04).
   • Use a debugger (GDB) to analyze the crash.

2. Crafting the Malicious EXR File:

   • Use a hex editor or a scripting language (Python) to modify an existing EXR file.
   • Focus on the EXR header fields that are processed by readChars(), such as attribute names or string data.
   • Increase the length of a string field beyond the expected buffer size.

3. Triggering the Overflow:

   • Write a simple C program that uses FreeImage to load the crafted EXR file.
   • Run the program under GDB to observe the crash and confirm the overflow.

4. Potential Code Execution:

   • If the overflow allows overwriting a return address or function pointer, craft a payload to achieve arbitrary code execution.

Blue Team (Detection & Defense)

1. Prevention:

   • Disable EXR format support in applications using FreeImage if not needed.
   • Use input validation and sandboxing for image processing.

2. Detection:

   • Monitor for crashes in applications that use FreeImage.
   • Use file scanning tools to detect malformed EXR files.

3. Response:

   • Isolate affected systems.
   • Analyze crash dumps to identify the malicious file.

Indicators of Compromise (IOCs)

• File Hashes: (No specific hashes available; generic IOC)
  • Malicious EXR files with unusually large string fields in headers.
• Behavioral IOCs:
  • Application crashes when opening EXR files.
  • Memory corruption errors in logs.
• Network IOCs:
  • Delivery of EXR files via email or download.

Detection Engineering

YARA Rule

rule CVE_2024_28564_FreeImage_EXR_BOF {
    meta:
        description = "Detects malicious EXR files targeting CVE-2024-28564"
        author = "Valters IT"
        date = "2024-01-01"
        reference = "CVE-2024-28564"
    strings:
        $exr_magic = { 76 2F 31 01 } // EXR magic bytes (little-endian)
        $long_string = /[\x00-\xFF]{256,}/ // Strings longer than 255 bytes
    condition:
        $exr_magic at 0 and #long_string > 0
}

Sigma Rule

title: CVE-2024-28564 FreeImage EXR Buffer Overflow
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects application crashes caused by malicious EXR files
author: Valters IT
date: 2024/01/01
logsource:
    category: application
    product: windows
detection:
    selection:
        EventID: 1000 (Application Error)
        Image: '*freeimage*'
    condition: selection
falsepositives:
    - Legitimate EXR files with large headers
level: medium

Suricata Rule

alert http any any -> any any (msg:"CVE-2024-28564 FreeImage EXR Buffer Overflow"; flow:to_client; fileext:"exr"; content:"|76 2F 31 01|"; distance:0; within:4; pcre:"/[\x00-\xFF]{256,}/R"; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate Mitigation:

   • Disable EXR format support in applications using FreeImage.
   • Use a different image processing library for EXR files.

2. Long-term Fix:

   • Apply the official patch when released by the FreeImage project.
   • Monitor the FreeImage repository for updates.

3. Workarounds:

   • Implement input validation to reject EXR files with unusually large string fields.
   • Use memory-safe languages or libraries for image processing.

4. Detection:

   • Deploy the provided YARA, Sigma, and Suricata rules to detect malicious EXR files.

Valters IT
DevSecOps & Cyber Threat Intelligence Expert