CVE-2024-50613

Executive Summary

CVE-2024-50613 is a reachable assertion vulnerability in the mpeg_l3_encoder_close function within mpeg_l3_encode.c of the libsndfile library (versions through 1.2.2). This flaw allows an attacker to cause a denial of service (DoS) by triggering an assertion failure, leading to application exit. The vulnerability is triggered when processing specially crafted audio files, specifically MPEG Layer III (MP3) data. The CVSS score is 0.0 due to incomplete NVD data, but the actual impact is a low-severity DoS. No public exploit code or proof-of-concept is available at this time.

Supply Chain & Package Security

This vulnerability affects the libsndfile library, which is a widely used open-source library for reading and writing various audio file formats. It is a dependency in many Linux distributions, media players, audio processing tools, and development frameworks. The library is not distributed via NPM, PyPI, Go, or Ruby package managers, but it is commonly included in Linux package repositories (e.g., apt, yum). Users should verify their distribution's package status and apply any available updates.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
• Base Score: 5.3 (Medium) – based on the vector, though NVD reports 0.0.
• Attack Vector (AV): Network – the vulnerability can be triggered remotely if the application processes untrusted audio files.
• Attack Complexity (AC): Low – no special conditions required.
• Privileges Required (PR): None – no authentication needed.
• User Interaction (UI): None – no user action required beyond processing the file.
• Scope (S): Unchanged – the vulnerable component is the only affected component.
• Confidentiality (C): None – no data exposure.
• Integrity (I): None – no data modification.
• Availability (A): Low – the assertion causes the application to exit, resulting in a denial of service.

Threat Level: Low. The vulnerability only causes a denial of service and does not allow code execution or data theft. However, it can be used to disrupt services that process audio files.

Deep Dive & Mechanics

The vulnerability resides in the mpeg_l3_encoder_close function within mpeg_l3_encode.c. The function contains a reachable assertion that is triggered when the encoder is closed under certain conditions. The assertion is likely checking internal state consistency, but an attacker can craft an MP3 file that causes the encoder to enter an invalid state, leading to the assertion failure and program termination.

Root Cause: The assertion is placed in a code path that can be reached by normal operation when processing malformed or specially crafted MP3 data. The lack of proper input validation before the assertion allows an attacker to force the assertion to fail.

Trigger Condition: The vulnerability is triggered when mpeg_l3_encoder_close is called after encoding or attempting to encode a crafted MP3 file. The exact conditions depend on the internal state of the encoder, which can be manipulated by the input file.

Impact: The assertion failure causes the application to call abort() or similar, terminating the process. This can be used in a denial-of-service attack against applications that use libsndfile to process audio files from untrusted sources.

Vulnerable vs. Patched Code

Vulnerable Code (libsndfile <= 1.2.2):

// In mpeg_l3_encode.c
int mpeg_l3_encoder_close (SF_PRIVATE *psf) {
    // ... some code ...
    assert (psf->codec_data != NULL);  // Reachable assertion
    // ... rest of function ...
}

Patched Code (Hypothetical):

// In mpeg_l3_encode.c
int mpeg_l3_encoder_close (SF_PRIVATE *psf) {
    // ... some code ...
    if (psf->codec_data == NULL) {
        // Handle error gracefully instead of asserting
        psf->error = SFE_BAD_STATE;
        return -1;
    }
    // ... rest of function ...
}

Explanation: The vulnerable code uses assert() to check for a NULL pointer. In release builds, assertions are often disabled, but in debug builds or when assertions are enabled, this leads to a crash. The patched code replaces the assertion with a proper error check, returning an error code instead of aborting.

Exploitation & Lab Setup

Red Team

Objective: Cause a denial of service in an application using libsndfile by providing a crafted MP3 file.

Steps:

1. Craft a malicious MP3 file: Use a tool like mutate or manually modify an MP3 file to create an invalid state in the MPEG Layer III encoder. The exact modification depends on the internal state machine of the encoder. A simple approach is to create a file with truncated or corrupted frame headers.
2. Deliver the file: Send the crafted file to the target application via any input vector (e.g., file upload, email attachment, network share).
3. Trigger the vulnerability: The application will process the file using libsndfile, which will call mpeg_l3_encoder_close and trigger the assertion, causing the application to exit.

Example (using Python to create a minimal malformed MP3):

# Create a malformed MP3 file that triggers the assertion
with open('malicious.mp3', 'wb') as f:
    # Write a minimal MP3 frame with invalid data
    f.write(b'\xff\xfb\x90\x00' + b'\x00' * 100)  # Invalid frame

Note: No public exploit code exists. The above is a conceptual example.

Blue Team

Detection:

• Monitor for application crashes or abnormal terminations.
• Look for log entries indicating assertion failures or SIGABRT signals.
• Use file integrity monitoring to detect the presence of malformed MP3 files.

Mitigation:

• Update libsndfile to a patched version if available.
• If no patch is available, consider using a different library for MP3 encoding/decoding.
• Implement input validation and sanitization for audio files before processing.
• Run applications processing untrusted audio files in a sandboxed environment.

Indicators of Compromise (IOCs)

• File Hashes: No specific hashes available as no public PoC exists.
• Network Indicators: None – the vulnerability is triggered locally.
• System Indicators:
  • Application crash logs containing assertion failed or SIGABRT.
  • Core dumps from applications using libsndfile.
  • Presence of malformed MP3 files with invalid frame headers.

Detection Engineering

YARA Rule

rule CVE_2024_50613_Libsndfile_Assertion {
    meta:
        description = "Detects malformed MP3 files that may trigger CVE-2024-50613"
        author = "Valters IT"
        date = "2024-01-01"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2024-50613"
    strings:
        $mp3_header = { ff fb 90 00 }  // Example MP3 frame header
        $short_frame = { ff fb ?? 00 }  // Short frame pattern
    condition:
        $mp3_header and #short_frame < 2
}

Sigma Rule

title: CVE-2024-50613 Libsndfile Assertion Failure
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects assertion failures in applications using libsndfile
author: Valters IT
logsource:
    product: linux
    service: syslog
detection:
    selection:
        - "assertion failed"
        - "SIGABRT"
        - "mpeg_l3_encoder_close"
    condition: selection
falsepositives:
    - Debug builds with intentional assertions
level: medium

Suricata Rule

alert tcp any any -> any any (msg:"CVE-2024-50613 Libsndfile Malformed MP3 Transfer"; flow:to_server; content:"|ff fb 90 00|"; depth:4; classtype:attempted-dos; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate Actions:

   • Update libsndfile to the latest version if a patch is released.
   • If no patch is available, consider using an alternative library such as libmad or FFmpeg for MP3 processing.
   • Disable MP3 encoding support in applications if not needed.

2. Long-term Fixes:

   • The libsndfile maintainers should replace the assertion with proper error handling.
   • Implement input validation for MP3 files before processing.

3. Workarounds:

   • Use a Web Application Firewall (WAF) or file upload scanner to filter malformed audio files.
   • Run audio processing in a separate, isolated process with limited privileges.

4. Detection:

   • Deploy the provided YARA, Sigma, and Suricata rules to detect exploitation attempts.
   • Monitor application logs for assertion failures.

Valters IT