CVE-2024-41217

Executive Summary

CVE-2024-41217 is a heap-based buffer overflow vulnerability discovered in tsMuxer, a popular tool for multiplexing and demultiplexing MPEG-TS streams. The flaw resides in the nightly build version nightly-2024-05-10-02-00-45 and is triggered when processing a specially crafted MKV video file. Successful exploitation allows an attacker to cause a Denial of Service (DoS) by corrupting heap memory, leading to application crashes or potential arbitrary code execution in certain scenarios. The vulnerability has a CVSS score of 0.0 (placeholder) and no known public exploit code or patch at the time of analysis. The EPSS score is 0.0%, indicating low exploitation likelihood in the wild, but the risk remains for users processing untrusted MKV files.

Supply Chain & Package Security

tsMuxer is not distributed via mainstream package managers like NPM, PyPI, Go, or Ruby. It is typically compiled from source or downloaded as a binary from the official GitHub repository. Users should verify the integrity of downloaded binaries and consider building from source with security flags enabled.

CVSS Breakdown & Threat Level

• CVSS Score: 0.0 (placeholder – actual score pending NVD analysis)
• Attack Vector: Local (requires user to open a malicious MKV file)
• Attack Complexity: Low
• Privileges Required: None
• User Interaction: Required (victim must open the file)
• Scope: Unchanged
• Confidentiality Impact: None (primarily DoS)
• Integrity Impact: None
• Availability Impact: High (application crash)
• Threat Level: Medium (due to low complexity and potential for DoS)

Deep Dive & Mechanics

The vulnerability is a classic heap-based buffer overflow (CWE-122) in tsMuxer's MKV parsing logic. When processing a crafted MKV file, the application fails to properly validate the size of data written to a heap-allocated buffer. An attacker can embed a malicious segment within the MKV container that, when parsed, writes beyond the allocated buffer boundary. This corrupts adjacent heap metadata, leading to a crash (DoS). In some cases, careful manipulation could allow overwriting function pointers or other critical data, potentially enabling code execution.

The root cause is likely insufficient bounds checking in the code that handles MKV cluster or block data. The overflow occurs during the demuxing process when tsMuxer attempts to copy data from the file into a fixed-size heap buffer without verifying the input length.

Vulnerable vs. Patched Code

Since no official patch is available, the vulnerable code path is identified in the nightly build. A hypothetical fix would involve adding size validation before memory copy operations.

Vulnerable Code (pseudo):

void parse_mkv_block(uint8_t *input, size_t input_len) {
    uint8_t *buffer = malloc(1024);
    // No bounds check
    memcpy(buffer, input, input_len);
}

Patched Code (pseudo):

void parse_mkv_block(uint8_t *input, size_t input_len) {
    size_t max_size = 1024;
    if (input_len > max_size) {
        // Handle error or truncate
        return;
    }
    uint8_t *buffer = malloc(max_size);
    memcpy(buffer, input, input_len);
}

Exploitation & Lab Setup

Red Team

1. Crafting the Malicious MKV: Use a fuzzer (e.g., AFL++) to generate a malformed MKV file that triggers the overflow. Alternatively, manually modify an MKV file's cluster block size field to exceed the expected buffer size.
2. Delivery: Host the crafted MKV on a website or send via email. Convince the target to open it with tsMuxer.
3. Trigger: When tsMuxer processes the file, the overflow occurs, causing a crash. For code execution, further heap grooming and ROP chain construction would be required.

Example command to test:

./tsmuxer crafted.mkv

Blue Team

1. Detection: Monitor for crashes of tsMuxer processes. Use file integrity monitoring to detect unexpected MKV files.
2. Prevention: Restrict execution of tsMuxer to trusted users. Use application whitelisting.
3. Mitigation: Run tsMuxer in a sandboxed environment (e.g., Docker with limited resources) to contain potential damage.

Indicators of Compromise (IOCs)

• File Hashes (SHA256): (None available – generate upon analysis)
• Process Anomalies: tsMuxer process crash with heap corruption error.
• Network: No network indicators (local file-based exploit).
• Logs: Application crash logs containing references to malloc, memcpy, or heap errors.

Detection Engineering

YARA Rule

rule CVE_2024_41217_tsMuxer_HeapOverflow {
    meta:
        description = "Detects crafted MKV files exploiting CVE-2024-41217"
        author = "Valters IT"
        date = "2025-01-01"
        reference = "CVE-2024-41217"
    strings:
        $magic = { 1A 45 DF A3 } // MKV header
        $cluster = { 1F 43 B6 75 } // Cluster element
        $block = { A1 } // Block element
        $overflow_size = /[\x00-\xff]{4}/ // Placeholder for oversized size field
    condition:
        $magic at 0 and $cluster and $block and #overflow_size > 1024
}

Sigma Rule

title: CVE-2024-41217 tsMuxer Heap Overflow Detection
id: 12345678-1234-1234-1234-123456789abc
status: experimental
description: Detects tsMuxer crashes due to heap overflow from crafted MKV files
author: Valters IT
logsource:
    category: application
    product: tsMuxer
detection:
    selection:
        EventID: 1000 (Application Error)
        Image: '*tsmuxer*'
        ExceptionCode: 0xc0000005 (Access Violation)
    condition: selection
falsepositives:
    - Legitimate crashes due to other bugs
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2024-41217 tsMuxer MKV Heap Overflow Attempt"; flow:to_server; file_data; content:"|1A 45 DF A3|"; distance:0; within:4; content:"|1F 43 B6 75|"; distance:0; within:4; content:"|A1|"; distance:0; within:1; byte_test:4,>,1024,0,relative; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate: Avoid opening MKV files from untrusted sources with tsMuxer nightly build nightly-2024-05-10-02-00-45.
2. Upgrade: Monitor the tsMuxer GitHub repository for a patched version. Once available, update immediately.
3. Workaround: Use alternative tools (e.g., FFmpeg) for MKV processing until a patch is released.
4. Compile from Source: If using tsMuxer, compile from source with AddressSanitizer (ASan) to detect heap overflows during development.
5. Sandboxing: Run tsMuxer in a restricted environment (e.g., Docker container with read-only filesystem) to limit impact.

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