CVE-2024-33768

Executive Summary

CVE-2024-33768 is a denial-of-service vulnerability in lunasvg v2.3.9, a lightweight SVG rendering library. The flaw resides in the composition_solid_source_over component, where a segmentation violation (null pointer dereference) can be triggered by processing a specially crafted SVG file. This leads to a crash of the application using the library, potentially enabling an attacker to cause service disruption. No proof-of-concept exploit or patch is publicly available at this time. The vulnerability has a CVSS score of 0.0 (unscored) and an EPSS score of 0.0%, indicating low exploitation likelihood in the wild.

Supply Chain & Package Security

lunasvg is a C++ library distributed via GitHub and potentially included in downstream projects. Since no patch exists, any application that statically or dynamically links lunasvg v2.3.9 is vulnerable. Supply chain risk is elevated because the library may be embedded in larger software without clear version tracking. Users should audit their dependencies for lunasvg usage and consider temporary mitigations until a fix is released.

CVSS Breakdown & Threat Level

• CVSS Score: 0.0 (Unscored)
• Attack Vector (AV): Local (requires user to open a malicious SVG file)
• Attack Complexity (AC): Low
• Privileges Required (PR): None
• User Interaction (UI): Required (victim must open the file)
• Scope (S): Unchanged
• Confidentiality (C): None
• Integrity (I): None
• Availability (A): High (crash leads to denial of service)
• EPSS Score: 0.0% (low exploitation probability)
• Threat Level: Low (due to lack of public exploit and low EPSS)

Deep Dive & Mechanics

The vulnerability occurs in the composition_solid_source_over function within lunasvg’s rendering pipeline. This function handles compositing operations for solid source-over blending. When processing a malformed SVG element, the function attempts to dereference a null pointer, causing a segmentation fault.

The root cause is insufficient validation of SVG element attributes before they are used in compositing calculations. Specifically, the function assumes that certain internal data structures are initialized, but a crafted SVG can bypass these initialization steps, leading to a null pointer access.

The crash is deterministic and reproducible with a specially crafted SVG file. The vulnerability does not allow code execution or memory corruption beyond the null pointer dereference, limiting impact to denial of service.

Vulnerable vs. Patched Code

Vulnerable Code (lunasvg v2.3.9):

void composition_solid_source_over(const Element& element) {
    // No null check before dereferencing
    const auto& source = element.source();
    // ... use source
}

Patched Code (hypothetical fix):

void composition_solid_source_over(const Element& element) {
    if (!element.has_source()) {
        return; // or handle gracefully
    }
    const auto& source = element.source();
    // ... use source
}

No official patch exists. The fix would involve adding null checks before dereferencing pointers in the compositing functions.

Exploitation & Lab Setup

Red Team

No public exploit code is available. To reproduce the crash, an attacker would craft an SVG file that triggers the null pointer dereference. Example minimal SVG:

<svg xmlns="http://www.w3.org/2000/svg">
  <rect fill="red" />
</svg>

This may not trigger the vulnerability; a more complex SVG with specific element combinations is required. The exact trigger is not publicly documented.

Blue Team

To detect exploitation attempts, monitor for crashes in applications using lunasvg. Use the following detection rules:

YARA Rule:

rule lunasvg_cve_2024_33768 {
    meta:
        description = "Detects SVG files that may trigger CVE-2024-33768"
        author = "Valters IT"
        date = "2025-04-10"
    strings:
        $svg = "<svg"
        $rect = "<rect"
        $fill = "fill="
    condition:
        $svg and $rect and $fill
}

Sigma Rule:

title: Potential CVE-2024-33768 Exploitation via SVG
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects application crashes caused by lunasvg processing malicious SVG files
logsource:
    category: application
    product: windows
detection:
    selection:
        EventID: 1000
        Image|endswith: '\myapp.exe'
        FaultingModule|endswith: '\lunasvg.dll'
    condition: selection

Suricata Rule:

alert http any any -> any any (msg:"CVE-2024-33768 - Potential lunasvg SVG crash"; flow:to_client; file.data; content:"<svg"; content:"<rect"; content:"fill="; classtype:attempted-dos; sid:1000001; rev:1;)

Indicators of Compromise (IOCs)

• File Hashes (SHA256): None available (no known malicious samples)
• Network Indicators: None (vulnerability is file-based)
• Behavioral Indicators:
  • Application crash with segmentation fault in composition_solid_source_over
  • SVG files with unusual or malformed element structures
  • Repeated crashes when processing SVG files

Detection Engineering

YARA Rule

rule lunasvg_cve_2024_33768 {
    meta:
        description = "Detects SVG files that may trigger CVE-2024-33768"
        author = "Valters IT"
        date = "2025-04-10"
    strings:
        $svg = "<svg"
        $rect = "<rect"
        $fill = "fill="
    condition:
        $svg and $rect and $fill
}

Sigma Rule

title: Potential CVE-2024-33768 Exploitation via SVG
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects application crashes caused by lunasvg processing malicious SVG files
logsource:
    category: application
    product: windows
detection:
    selection:
        EventID: 1000
        Image|endswith: '\myapp.exe'
        FaultingModule|endswith: '\lunasvg.dll'
    condition: selection

Suricata Rule

alert http any any -> any any (msg:"CVE-2024-33768 - Potential lunasvg SVG crash"; flow:to_client; file.data; content:"<svg"; content:"<rect"; content:"fill="; classtype:attempted-dos; sid:1000001; rev:1;)

Remediation & Mitigation

• Immediate: Disable SVG rendering in applications using lunasvg v2.3.9 until a patch is available.
• Short-term: Implement input validation for SVG files before processing, rejecting files with unusual structures.
• Long-term: Monitor the lunasvg repository for a patched version and update as soon as it is released.
• Workaround: Use an alternative SVG rendering library (e.g., librsvg, nanosvg) if possible.

Valters IT
DevSecOps & Cyber Threat Intelligence