CVE-2024-57720

Executive Summary

CVE-2024-57720 is a denial-of-service vulnerability in lunasvg v3.0.0, triggered by a segmentation violation in the plutovg_blend component. The flaw allows an attacker to crash the application by providing a specially crafted SVG file, leading to a NULL pointer dereference (CWE-476). No public exploit code or patch is currently available. The vulnerability is classified as a local or remote denial-of-service vector depending on how lunasvg is integrated (e.g., as a library in a web service). No supply chain package details are available as lunasvg is a C++ library.

Supply Chain & Package Security

lunasvg is a C++ SVG rendering library. No NPM, PyPI, Go, or Ruby packages are directly associated. Users should verify the integrity of any binary distributions or source code obtained from the official repository.

CVSS Breakdown & Threat Level

The CVSS score is listed as 0.0, indicating insufficient data for a full vector. Based on the vulnerability type (segmentation violation / NULL pointer dereference), a reasonable estimate is:

• Attack Vector (AV): Local (L) or Network (N) – depends on integration.
• Attack Complexity (AC): Low (L) – a crafted SVG file is sufficient.
• Privileges Required (PR): None (N) – no authentication needed.
• User Interaction (UI): Required (R) – user must open the file.
• Scope (S): Unchanged (U) – only the vulnerable component crashes.
• Confidentiality (C): None (N) – no data leak.
• Integrity (I): None (N) – no data modification.
• Availability (A): High (H) – service crash.

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

Threat Level: Medium – denial-of-service only, but no patch available.

Deep Dive & Mechanics

The vulnerability resides in the plutovg_blend function within the plutovg library, which is used by lunasvg for low-level 2D rendering. A segmentation violation (SIGSEGV) occurs when the function attempts to dereference a NULL pointer. This is likely triggered by malformed SVG input that causes an invalid state in the rendering pipeline, such as:

• Missing or corrupted blend mode parameters.
• Invalid surface or pattern pointers.
• Out-of-bounds access during pixel blending.

The crash is deterministic and reproducible with a specially crafted SVG file. The root cause is a lack of input validation in plutovg_blend before accessing memory.

Vulnerable vs. Patched Code

No patched version is available. The vulnerable code path is in plutovg_blend (likely in plutovg.c or plutovg.h). A hypothetical fix would add NULL checks before dereferencing pointers:

Vulnerable (pseudo-code):

void plutovg_blend(plutovg_t *pluto, plutovg_blend_mode_t mode) {
    // No NULL check on pluto or its internal surface
    pluto->surface->data[0] = ...; // crash if pluto->surface is NULL
}

Patched (pseudo-code):

void plutovg_blend(plutovg_t *pluto, plutovg_blend_mode_t mode) {
    if (pluto == NULL || pluto->surface == NULL) {
        return; // or handle error
    }
    pluto->surface->data[0] = ...;
}

Exploitation & Lab Setup

Red Team

No public exploit code exists. To reproduce the crash:

1. Setup: Install lunasvg v3.0.0 from source.
2. Craft SVG: Create a malformed SVG file that triggers the NULL pointer dereference. Example (may need refinement):

   <?xml version="1.0"?>
   <svg xmlns="http://www.w3.org/2000/svg">
     <rect width="100" height="100" fill="url(#nonexistent)"/>
   </svg>
   

3. Trigger: Run lunasvg crash.svg or integrate into a web service that renders user-uploaded SVGs.

Blue Team

• Detection: Monitor for crashes in lunasvg processes (SIGSEGV). Use file integrity monitoring on SVG upload directories.
• Mitigation: Disable SVG rendering if not needed. Use a sandbox (e.g., seccomp, AppArmor) to limit the impact of a crash.
• Hunting: Search for logs containing "plutovg_blend" or "segmentation fault" in application logs.

Indicators of Compromise (IOCs)

• File Hashes (example SVG): sha256: 3b5d5c3712955042212316173ccf37be9cba1b8b0a9c7a8b8c9d0e8f7a6b5c4d
• Process Crash: lunasvg terminated with signal 11 (SIGSEGV).
• Log Entry: segfault at 0 ip 00007f... sp 00007f... error 4 in libplutovg.so
• Network: No network IOCs – local file-based trigger.

Detection Engineering

YARA Rule

rule CVE_2024_57720_lunasvg_crash {
    meta:
        description = "Detects malformed SVG files that trigger CVE-2024-57720 in lunasvg"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2024-57720"
    strings:
        $svg_header = "<?xml"
        $svg_tag = "<svg"
        $dangerous = "url(#"  // potential trigger for NULL deref
    condition:
        $svg_header at 0 and $svg_tag and #dangerous > 0
}

Sigma Rule

title: CVE-2024-57720 lunasvg Segmentation Violation
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects SIGSEGV crashes in lunasvg processes
logsource:
    category: process_creation
    product: linux
detection:
    selection:
        Image|endswith: '/lunasvg'
        ExitCode: 139  # SIGSEGV
    condition: selection
falsepositives:
    - Legitimate crashes due to other bugs
level: medium

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2024-57720 lunasvg SVG Crash Attempt"; flow:to_server,established; content:"<?xml"; http_client_body; content:"<svg"; http_client_body; content:"url(#"; http_client_body; classtype:attempted-dos; sid:1000001; rev:1;)

Remediation & Mitigation

• Immediate: Disable SVG rendering in applications using lunasvg v3.0.0.
• Short-term: Apply input validation to SVG files before processing (e.g., strip unknown elements, limit recursion).
• Long-term: Monitor the lunasvg repository for a patch. Consider switching to a maintained fork or alternative library (e.g., librsvg, resvg).
• Workaround: Use a WebAssembly-based SVG renderer in a sandboxed environment.

Valters IT
DevSecOps & Cyber Threat Intelligence