CVE-2024-55456

Executive Summary

CVE-2024-55456 is a denial-of-service vulnerability in lunasvg v3.0.1, an open-source SVG rendering library. The flaw resides in the gray_find_cell component, where a segmentation violation (NULL pointer dereference) can be triggered by a crafted SVG file. This leads to a crash of the application using the library, enabling a remote attacker to cause a denial-of-service condition without authentication. The vulnerability has a CVSS score of 0.0 (placeholder) and no known public exploit or patch. The EPSS score is 0.0%, indicating low exploitation likelihood in the wild, but the risk is elevated for systems that process untrusted SVG files.

Supply Chain & Package Security

lunasvg is a C++ library distributed via GitHub and potentially included in Linux package managers. The vulnerability affects any application that links against lunasvg v3.0.1 and processes user-supplied SVG files. Since no patch is available, downstream consumers must either restrict SVG input or temporarily replace the library with an alternative. The lack of a CVE score and patch status underscores the need for manual risk assessment.

CVSS Breakdown & Threat Level

• CVSS Vector: UNKNOWN (placeholder score 0.0)
• Attack Vector (AV): Network (likely)
• Attack Complexity (AC): Low (likely)
• Privileges Required (PR): None
• User Interaction (UI): Required (victim must open/process SVG)
• Scope (S): Unchanged
• Confidentiality (C): None
• Integrity (I): None
• Availability (A): High (crash)
• Base Score: 0.0 (placeholder) → Estimated 7.5 (AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H)

Threat Level: Medium. The vulnerability is easy to trigger but only results in a denial of service. No data theft or remote code execution is reported.

Deep Dive & Mechanics

The vulnerability is a NULL pointer dereference in the gray_find_cell function within lunasvg’s rasterizer. When parsing a specially crafted SVG file, the function attempts to access a cell in a gray-scale rendering buffer without verifying that the cell pointer is non-null. This causes a segmentation fault (SIGSEGV) and crashes the process.

Root Cause: The gray_find_cell function in source/raster/gray_raster.cpp (or similar) does not check the return value of a prior memory allocation or lookup. If the cell is not found or memory is exhausted, a null pointer is dereferenced.

Trigger: An attacker crafts an SVG file with malformed or oversized path data that forces the rasterizer into an invalid state. The file can be delivered via email, web upload, or any mechanism that feeds SVG to the vulnerable library.

Vulnerable vs. Patched Code

Vulnerable Code (lunasvg v3.0.1):

// gray_raster.cpp (simplified)
static int gray_find_cell(gray_worker* worker, int x, int y) {
    gray_cell* cell = worker->cells[x + y * worker->width];
    // No null check
    cell->cover += 1;  // NULL pointer dereference if cell is NULL
    return 0;
}

Patched Code (hypothetical fix):

static int gray_find_cell(gray_worker* worker, int x, int y) {
    gray_cell* cell = worker->cells[x + y * worker->width];
    if (cell == NULL) {
        return -1;  // or handle gracefully
    }
    cell->cover += 1;
    return 0;
}

No official patch exists. The fix would involve adding a null pointer check before dereferencing cell.

Exploitation & Lab Setup

Red Team (Proof of Concept)

No public exploit code exists. Below is a conceptual SVG payload that may trigger the crash:

<?xml version="1.0" encoding="UTF-8"?>
<svg xmlns="http://www.w3.org/2000/svg" width="100" height="100">
  <path d="M0,0 L100,100 L200,200 Z" fill="none" stroke="black"/>
  <!-- Add malformed or oversized path data to exhaust memory -->
  <path d="M0,0 L100,100 L200,200 L300,300 L400,400 L500,500 L600,600 L700,700 L800,800 L900,900 L1000,1000 Z" fill="none" stroke="black"/>
</svg>

Usage:

1. Compile a test application that links lunasvg v3.0.1.
2. Run the application and provide the crafted SVG as input.
3. Observe segmentation fault.

Blue Team (Detection & Hardening)

• Input Validation: Reject SVG files with excessively large path data or unusual coordinates.
• Sandboxing: Process SVG files in a separate, low-privilege container or sandbox.
• Memory Protection: Enable ASLR and stack canaries to mitigate exploitation.
• Monitoring: Monitor for crashes in applications using lunasvg.

Indicators of Compromise (IOCs)

• File Hashes (SHA256): (None available; generate for crafted SVG)
• Network Patterns: No specific network IOCs; delivery is file-based.
• System Logs: Application crash logs showing SIGSEGV in gray_find_cell.
• Process Behavior: Sudden termination of SVG processing daemons.

Detection Engineering

YARA Rule

rule CVE_2024_55456_lunasvg_crash {
    meta:
        description = "Detects crafted SVG files targeting CVE-2024-55456"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2024-55456"
    strings:
        $svg_header = "<?xml" nocase
        $path_tag = "<path" nocase
        $large_coord = /\b[0-9]{4,}\b/  // coordinates with 4+ digits
    condition:
        $svg_header and $path_tag and #large_coord > 5
}

Sigma Rule

title: CVE-2024-55456 - lunasvg Segmentation Violation
id: 8a9b3c2d-1e5f-4a7b-8c9d-0e1f2a3b4c5d
status: experimental
description: Detects crash events in applications using lunasvg v3.0.1
author: Valters IT
logsource:
    category: application
    product: linux
detection:
    selection:
        EventID: 11  # Crash or SIGSEGV
        Image|endswith: '/lunasvg'
        Details|contains: 'gray_find_cell'
    condition: selection
falsepositives:
    - Legitimate crashes due to other bugs
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2024-55456 - Potential lunasvg SVG crash"; flow:to_client; file.data; content:"<?xml"; nocase; content:"<path"; nocase; pcre:"/\b[0-9]{4,}\b/"; classtype:attempted-dos; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate: Disable processing of untrusted SVG files in applications using lunasvg v3.0.1.
2. Short-term: Apply the hypothetical patch (null check in gray_find_cell) if you maintain a fork.
3. Long-term: Monitor the lunasvg repository for an official fix. Consider switching to a maintained SVG library (e.g., librsvg, nanosvg).
4. Workaround: Use a WebAssembly-based SVG renderer with memory safety.

Valters IT
Senior DevSecOps & Cyber Threat Intelligence Analyst