CVE-2025-63757: FFmpeg Buffer Overflow Vulnerability

CVE-2025-63757 Overview

CVE-2025-63757 is an integer overflow vulnerability discovered in the yuv2ya16_X_c_template function within libswscale/output.c in FFmpeg version 8.0. This vulnerability affects the software scaling library component of FFmpeg, which is widely used for video and image processing operations. The integer overflow condition can be triggered when processing specially crafted media files, potentially leading to denial of service conditions.

Critical Impact

Successful exploitation of this integer overflow vulnerability can cause application crashes and denial of service, affecting any system or application that relies on FFmpeg for media processing.

Affected Products

• FFmpeg version 8.0
• Applications and services utilizing FFmpeg 8.0 for media transcoding
• Video streaming platforms using vulnerable FFmpeg builds

Discovery Timeline

• 2025-12-18 - CVE-2025-63757 published to NVD
• 2025-12-30 - Last updated in NVD database

Technical Details for CVE-2025-63757

Vulnerability Analysis

This vulnerability is classified as CWE-190: Integer Overflow or Wraparound. The flaw exists within the yuv2ya16_X_c_template function, which is responsible for converting YUV color space data to YA16 (grayscale with alpha channel in 16-bit precision) format during scaling operations. When processing certain input parameters, the function performs arithmetic operations that can exceed the maximum value representable by the integer data type, causing the value to wrap around to an unexpected small or negative number.

The integer overflow condition can be exploited remotely through network-delivered media files. An attacker can craft a malicious video or image file that, when processed by FFmpeg, triggers the overflow condition in the scaling library. This can lead to incorrect memory allocation sizes, buffer operations with unexpected lengths, and ultimately application crashes or hangs, resulting in denial of service.

Root Cause

The root cause of this vulnerability lies in insufficient validation of arithmetic operations within the yuv2ya16_X_c_template function. When calculating buffer sizes or pixel coordinates during the YUV to YA16 conversion process, the code fails to properly check whether the intermediate or final values exceed integer bounds before performing the calculation. This allows specially crafted input dimensions or parameters to trigger an overflow condition.

Attack Vector

The attack vector for CVE-2025-63757 is network-based, requiring no user interaction or special privileges. An attacker can exploit this vulnerability by:

1. Crafting a malicious media file (video or image) with specific dimensions or encoding parameters designed to trigger the integer overflow
2. Delivering the malicious file to a target system via web application, email attachment, or network stream
3. When the target system processes the file using FFmpeg 8.0 for transcoding, thumbnail generation, or playback, the vulnerable function is invoked
4. The integer overflow occurs during color space conversion, leading to denial of service

The vulnerability specifically affects the libswscale component responsible for software-based scaling and pixel format conversion. Technical details and additional context are available in the FFmpeg Pull Request addressing this issue.

Detection Methods for CVE-2025-63757

Indicators of Compromise

• Unexpected FFmpeg process crashes or terminations during media processing operations
• Abnormal memory usage patterns or allocation failures in FFmpeg-dependent applications
• Error logs indicating failures in libswscale operations or color space conversion functions
• Media files with unusual or malformed dimension metadata causing processing failures

Detection Strategies

• Deploy runtime application monitoring to detect abnormal FFmpeg process behavior and crashes
• Implement file integrity monitoring on media processing pipelines to identify malicious input files
• Configure application crash dump analysis to identify exploitation attempts targeting the yuv2ya16_X_c_template function
• Use static analysis tools to scan for vulnerable FFmpeg 8.0 installations across the environment

Monitoring Recommendations

• Enable detailed logging for FFmpeg operations, particularly scaling and format conversion functions
• Monitor system resources for unexpected memory allocation patterns in media processing workflows
• Set up alerting for repeated FFmpeg process failures that may indicate exploitation attempts
• Track media file processing metrics to identify anomalous files that cause failures

How to Mitigate CVE-2025-63757

Immediate Actions Required

• Identify all systems and applications using FFmpeg 8.0 and prioritize them for patching
• Implement input validation for media files processed by FFmpeg to filter potentially malicious content
• Consider temporarily disabling or restricting access to media processing functionality until patches are applied
• Monitor FFmpeg processes for abnormal behavior and crashes

Patch Information

A fix for this vulnerability has been submitted to the FFmpeg project. Organizations should monitor the FFmpeg Security Overview page for official security announcements and update to a patched version when available. The specific fix can be reviewed in the FFmpeg Pull Request #20698.

Workarounds

• Implement strict input validation to reject media files with unusual or extreme dimension parameters
• Deploy FFmpeg within a sandboxed environment to contain potential denial of service impacts
• Use Web Application Firewalls (WAF) or content filtering to inspect and block malicious media uploads
• Consider using alternative media processing libraries for critical workflows until the patch is applied

# Example: Sandboxing FFmpeg with resource limits
# Limit memory and CPU to contain DoS impact
ulimit -v 2097152  # Limit virtual memory to 2GB
ulimit -t 300      # Limit CPU time to 5 minutes
ffmpeg -i input.mp4 -vf scale=1920:1080 output.mp4