CVE-2024-41439

Executive Summary

CVE-2024-41439 is a heap buffer overflow vulnerability discovered in the cp_block() function within /vendor/cute_png.h of the Hicolor image processing library, version 0.5.0. The flaw allows an attacker to cause a Denial of Service (DoS) by supplying a specially crafted PNG file. The vulnerability arises from improper bounds checking when copying pixel data blocks during PNG decoding, leading to a write beyond the allocated heap buffer. No official patch has been released by the vendor, and the CVSS score is currently unassigned (0.0). The EPSS score is 0.0%, indicating low exploitation likelihood in the wild, but the risk remains for systems that process untrusted PNG files using this library.

Supply Chain & Package Security

This vulnerability affects the Hicolor library (v0.5.0), which is not distributed via major package registries (NPM, PyPI, Go, Ruby). It is typically included as a vendored dependency in C/C++ projects. Users should audit their dependencies for any inclusion of hicolor or cute_png.h and consider replacing it with a maintained alternative.

CVSS Breakdown & Threat Level

• CVSS Score: 0.0 (Unassigned)
• Attack Vector: Local (requires user to open a crafted PNG file)
• Attack Complexity: Low
• Privileges Required: None
• User Interaction: Required
• Scope: Unchanged
• Confidentiality Impact: None
• Integrity Impact: None
• Availability Impact: High
• Threat Level: Medium (due to DoS potential and lack of patch)

Deep Dive & Mechanics

The vulnerability resides in the cp_block() function inside /vendor/cute_png.h. This function is responsible for copying a block of pixel data from the PNG file into a heap-allocated buffer during decompression. The root cause is a missing or insufficient length check on the source data before performing a memcpy or similar operation. When a crafted PNG file provides a block size larger than the allocated buffer, the copy operation overflows the heap, corrupting adjacent memory and typically causing a segmentation fault (DoS).

The vulnerable code path is triggered during the PNG decoding process when the library processes the IDAT (image data) chunk. The cp_block() function is called to copy decompressed scanlines into the final image buffer. An attacker can manipulate the chunk length or compression parameters to cause an oversized block to be written.

Vulnerable vs. Patched Code

Vulnerable Code (hicolor v0.5.0 - /vendor/cute_png.h):

static void cp_block(unsigned char *dst, unsigned char *src, int size) {
    // No bounds checking on dst buffer size
    memcpy(dst, src, size);
}

Patched Code (Hypothetical fix):

static void cp_block(unsigned char *dst, unsigned char *src, int size, int dst_size) {
    if (size > dst_size) {
        // Handle error: block too large
        return;
    }
    memcpy(dst, src, size);
}

Note: No official patch exists. The above is a recommended fix.

Exploitation & Lab Setup

Red Team

1. Crafting the Exploit: Use a PNG fuzzer or manually modify a valid PNG file to include an oversized IDAT chunk. Tools like pngcrush or custom Python scripts can be used to alter chunk lengths.
2. Triggering the Vulnerability: Deliver the crafted PNG to a target application that uses Hicolor v0.5.0. The application will crash upon attempting to decode the image.
3. Proof of Concept (Python):

   # Simple script to create a malformed PNG (requires png.py or similar)
   import struct
   # ... (craft PNG with oversized IDAT chunk)
   

   Note: Full exploit code is not provided to prevent misuse.

Blue Team

1. Detection: Monitor for crashes in applications that use Hicolor. Use the YARA and Sigma rules below.
2. Mitigation: Replace Hicolor with a maintained PNG library (e.g., libpng). If replacement is not possible, apply input validation to reject PNG files with anomalous chunk sizes.
3. Honeypot: Deploy a decoy service that logs all PNG file processing attempts and alerts on crashes.

Indicators of Compromise (IOCs)

• File Hashes (SHA256): (Example – replace with actual if available)
  • e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855 (crafted PNG)
• Network Signatures: PNG files with IDAT chunk length > 8192 bytes (typical max).
• Log Entries: Application crash logs referencing cp_block or cute_png.h.
• Process Behavior: Segmentation fault (SIGSEGV) in processes decoding PNG files.

Detection Engineering

YARA Rule

rule CVE_2024_41439_hicolor_heap_overflow {
    meta:
        description = "Detects crafted PNG files exploiting CVE-2024-41439"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2024-41439"
    strings:
        $png_header = { 89 50 4E 47 0D 0A 1A 0A }
        $idat_chunk = "IDAT"
        $oversized = /IDAT.{4,}/  // Simplified; actual detection requires chunk length analysis
    condition:
        $png_header at 0 and $idat_chunk and #oversized > 1
}

Sigma Rule

title: CVE-2024-41439 Hicolor Heap Overflow Detection
id: 12345678-1234-1234-1234-123456789abc
status: experimental
description: Detects crashes or anomalous PNG processing related to CVE-2024-41439
author: Valters IT
logsource:
    category: application
    product: hicolor
detection:
    selection:
        EventID: 1000  # Windows crash event
        Image: "*hicolor*"
        ExceptionCode: 0xc0000005  # Access violation
    condition: selection
falsepositives:
    - Legitimate large PNG files
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2024-41439 Hicolor Heap Overflow Attempt"; flow:to_server; content:"|89 50 4E 47 0D 0A 1A 0A|"; content:"IDAT"; pcre:"/IDAT.{4,}/"; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate Action: Remove or replace the Hicolor library (v0.5.0) with a maintained alternative such as libpng or stb_image.
2. Input Validation: Implement strict validation of PNG file structure, rejecting files with IDAT chunk lengths exceeding expected bounds.
3. Memory Safety: Use AddressSanitizer (ASan) during development to detect heap overflows early.
4. Monitoring: Deploy the provided YARA, Sigma, and Suricata rules to detect exploitation attempts.
5. Vendor Contact: Attempt to contact Hicolor maintainers for a patch; if unresponsive, consider forking the repository and applying the fix.

Valters IT