CVE-2024-41438

Executive Summary

CVE-2024-41438 is a heap buffer overflow vulnerability discovered in the cp_stored() function within the file /vendor/cute_png.h 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 PNG decompression logic, where insufficient bounds checking on heap-allocated buffers can lead to memory corruption. As of this report, no official patch has been released, and the vendor status remains unknown. The EPSS score is 0.0%, indicating low exploitation activity in the wild, but the risk is elevated for applications that process untrusted PNG images using this library.

Supply Chain & Package Security

Hicolor is a C/C++ library used for image processing. It is not distributed via NPM, PyPI, Go, or Ruby registries. However, it may be included as a dependency in other software packages. Users should audit their software supply chain for any inclusion of Hicolor v0.5.0 and consider replacing it with a maintained alternative.

CVSS Breakdown & Threat Level

The CVSS score is listed as 0.0, but this is likely a placeholder. 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 the victim 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) – user must open the file.
• Scope (S): Unchanged (U) – vulnerability does not cross trust boundaries.
• Confidentiality (C): None (N) – no data leak.
• Integrity (I): None (N) – no data modification.
• Availability (A): High (H) – service crash.

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

Threat Level: Medium. Exploitation requires user interaction, but the impact is a denial of service. No public exploit code is available, reducing immediate risk.

Deep Dive & Mechanics

The vulnerability is located in the cp_stored() function within cute_png.h. This function handles the decompression of PNG image data stored in the "stored" (no compression) filter method. The heap buffer overflow occurs when the function fails to properly validate the size of the decompressed data against the allocated buffer.

Root Cause: The cp_stored() function reads the compressed data length from the PNG chunk header and allocates a heap buffer based on that length. However, it does not verify that the actual decompressed data size matches the expected size. A crafted PNG file can specify a small compressed data length but contain a larger amount of decompressed data, causing a heap buffer overflow when the function writes beyond the allocated buffer.

Attack Vector: An attacker crafts a PNG file with a manipulated IDAT chunk (or other data chunks) that triggers the overflow. The victim must open this file using an application that relies on Hicolor v0.5.0.

Impact: Successful exploitation leads to memory corruption, which can crash the application (DoS). In some cases, it might be leveraged for arbitrary code execution, but the primary risk is denial of service.

Vulnerable vs. Patched Code

Vulnerable Code (Hicolor v0.5.0 - cute_png.h):

static void cp_stored(png_t *png, unsigned char *out, unsigned char *in, unsigned int len) {
    unsigned int i;
    for (i = 0; i < len; i++) {
        out[i] = in[i];  // No bounds check on 'out' buffer
    }
}

Patched Code (Hypothetical fix):

static void cp_stored(png_t *png, unsigned char *out, unsigned char *in, unsigned int len) {
    unsigned int i;
    if (len > png->out_size) {
        // Handle error: decompressed data exceeds buffer
        return;
    }
    for (i = 0; i < len; i++) {
        out[i] = in[i];
    }
}

The fix adds a bounds check to ensure len does not exceed the allocated output buffer size (png->out_size). Without this check, an attacker can supply a len value larger than the buffer, causing an overflow.

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• Hicolor v0.5.0 library linked to a target application.
• Ability to deliver a crafted PNG file to the victim.

Exploit Steps:

1. Craft a malicious PNG file: Modify the IDAT chunk to specify a small compressed data length but include a larger decompressed payload. For example, set the chunk length to 10 bytes but include 1000 bytes of data.
2. Deliver the file: Use social engineering (e.g., email attachment, download link) to trick the victim into opening the file.
3. Trigger the overflow: When the application calls cp_stored(), the overflow occurs, corrupting heap memory and likely crashing the application.

Example Crafted PNG (Hex Dump):

89 50 4E 47 0D 0A 1A 0A  // PNG signature
00 00 00 0D 49 48 44 52  // IHDR chunk
... (valid IHDR data)
00 00 00 0A 49 44 41 54  // IDAT chunk with length 10
... (10 bytes of compressed data)
00 00 00 00 49 45 4E 44  // IEND chunk

Note: No public exploit code is available. This is a conceptual description.

Blue Team (Defense & Detection)

Detection:

• Monitor for crashes in applications using Hicolor v0.5.0.
• Use memory analysis tools (e.g., Valgrind, AddressSanitizer) to detect heap overflows during PNG processing.
• Implement file integrity monitoring for PNG files.

Mitigation:

• Replace Hicolor v0.5.0 with a patched version or alternative library.
• Use a Web Application Firewall (WAF) to block malicious file uploads.
• Sandbox image processing in a separate process with limited privileges.

Indicators of Compromise (IOCs)

• File Hashes (SHA256): (None available – no known malicious samples)
• Network Indicators: None – exploitation is local file-based.
• Behavioral Indicators:
  • Application crash when opening a PNG file.
  • Heap corruption errors in logs (e.g., *** glibc detected *** free(): invalid pointer).
  • Abnormal memory usage spikes during PNG decoding.

Detection Engineering

YARA Rule

rule CVE_2024_41438_HeapOverflow {
    meta:
        description = "Detects crafted PNG files targeting CVE-2024-41438"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2024-41438"
    strings:
        $png_header = { 89 50 4E 47 0D 0A 1A 0A }
        $idat_chunk = { 49 44 41 54 }
        $small_len = { 00 00 00 0A }  // Example: length 10
    condition:
        $png_header at 0 and $idat_chunk and $small_len
}

Sigma Rule

title: CVE-2024-41438 Heap Buffer Overflow in Hicolor
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects potential exploitation of CVE-2024-41438 via application crash logs
author: Valters IT
date: 2025-04-10
logsource:
    category: application
    product: linux
detection:
    selection:
        EventID: 1000  # Application Error (Windows) or similar
        Message|contains: "hicolor"
    condition: selection
falsepositives:
    - Legitimate crashes due to other bugs
level: medium

Suricata Rule

alert http any any -> any any (msg:"CVE-2024-41438 Potential PNG Heap Overflow"; flow:to_server; file_data; content:"|89 50 4E 47 0D 0A 1A 0A|"; content:"|49 44 41 54|"; distance:0; within:100; pcre:"/\\x00\\x00\\x00\\x0A/"; classtype:attempted-dos; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Isolate: Remove Hicolor v0.5.0 from production systems if possible.
2. Monitor: Enable detailed logging for applications that process PNG files.
3. Update: Check for any vendor patches or updates. If none, consider forking the library and applying the bounds check fix.

Long-Term Solutions:

• Replace Hicolor with a maintained library (e.g., libpng, stb_image).
• Implement input validation for PNG files (e.g., verify chunk sizes before processing).
• Use memory-safe languages or sandboxing for image parsing.

Workarounds:

• Disable PNG processing in applications that use Hicolor.
• Use a proxy to scan and reject suspicious PNG files.

Valters IT