A recent vulnerability (CVE-2025-0518) has been discovered in the FFmpeg software, which leaves it susceptible to an out-of-bounds read and unchecked return value. This vulnerability can potentially allow an attacker to read sensitive constants within an executable. FFmpeg, a popular open-source multimedia framework, is widely used for processing video and audio files. This post will delve into the details of this vulnerability, including the affected program files, the associated code snippets, and the fix implemented by the FFmpeg team.

Affected Program File

The vulnerability is specifically associated with the following program file within the FFmpeg project: https://github.com/FFmpeg/FFmpeg/blob/master/libavfilter/af_pan.c

This file is part of the libavfilter component, responsible for audio filtering tasks.

Affected FFmpeg Version

The vulnerability impacts FFmpeg version 7.1.

Issue Discovery

The issue originated from a discovery by Simcha Kosman, a security researcher.

Issue Details

The vulnerability in question consists of an unchecked return value from a function call and an out-of-bounds read issue. The problem arises due to the pan filter not properly validating input parameters, resulting in a read attempt at an out-of-bounds location. Here is a code snippet that exhibits the vulnerability within the af_pan.c file:

static av_cold int init(AVFilterContext *ctx)
{
    PanContext *pan = ctx->priv;
    int ret;

    if ((ret = parse_channel_expressions(ctx, )) < )
        return ret;

    return ;
}

The function parse_channel_expressions() is responsible for parsing channel expressions for audio panning. However, in the init() function, the return value of this function isn't checked. This oversight can lead to an out-of-bounds read vulnerability.

Issue Fix

The FFmpeg team fixed the vulnerability by implementing a proper check for the return value of the parse_channel_expressions() function. The fix is present in the following commit: https://github.com/FFmpeg/FFmpeg/commit/b5b6391d64807578ab872dc58fb8aa621dcfc38a

Here is the code snippet of the fix to offer a better understanding

static av_cold int init(AVFilterContext *ctx)
{
    PanContext *pan = ctx->priv;
    int ret;

    if ((ret = parse_channel_expressions(ctx, )) < )
        return ret;

    if (ret) {
        av_log(ctx, AV_LOG_ERROR, "Unable to parse channel expressions\n");
        return AVERROR(EINVAL);
    }

    return ;
}

This modification in the init() function checks the return value of the parse_channel_expressions() function and logs an error message if it is non-zero. This change prevents the out-of-bounds read vulnerability from being exploited.

Conclusion

The discovery and subsequent fix of the CVE-2025-0518 vulnerability helps ensure the continued security and reliability of the FFmpeg software. As with any open-source project, it is crucial for the community and security researchers to continuously evaluate the software for potential issues. The quick resolution of this vulnerability showcases the dedication of the FFmpeg team to providing robust software for video and audio processing tasks.

Timeline

Published on: 01/16/2025 17:15:12 UTC