CVE-2026-38347 in FFmpeg
Summary
by MITRE • 08/28/2026
A heap overflow in the ff_sws_alphablendaway function (libswscale/alphablend.c) of FFmpeg git-master commit 722a217 allows attackers to cause a Denial of Service (DoS) via a crafted input.
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Analysis
by VulDB Data Team • 08/28/2026
The vulnerability identified in the ff_sws_alphablendaway function within the libswscale/alphablend.c module of FFmpeg represents a critical heap-based buffer overflow condition. This specific component is responsible for handling alpha blending operations during video processing, where pixel data from multiple sources is combined based on transparency masks. The flaw arises when the function processes crafted input files that contain malformed or maliciously constructed header information and dimension parameters. Specifically, the issue stems from an incorrect calculation of memory allocation sizes relative to the actual amount of data being written into the heap buffer. When a user supplies video frames with dimensions or alpha channel configurations that exceed expected bounds without proper validation, the function allocates insufficient memory space before proceeding to copy pixel data. This discrepancy leads to writes extending beyond the allocated heap boundaries, corrupting adjacent memory structures and potentially overwriting critical control data such as metadata pointers or size fields associated with subsequent allocations.
From a technical perspective, this vulnerability is classified under CWE-122, which denotes a heap-based buffer overflow. The root cause lies in the failure to validate input parameters against internal limits before performing arithmetic operations that determine buffer sizes. In complex multimedia frameworks like FFmpeg, such errors are particularly dangerous because they can be triggered by simply opening or playing a specially crafted media file rather than requiring active user interaction beyond initial loading. The attacker exploits this logic error by constructing an input stream where the width and height values, combined with pixel format specifics, result in a calculated buffer size that is smaller than the actual data payload required for processing. Consequently, when the blending algorithm executes its core operations, it writes past the end of the heap block, leading to memory corruption. This type of exploitation does not necessarily require remote code execution capabilities immediately but serves as a reliable vector for causing application instability and crashes.
The operational impact of this vulnerability is primarily centered on Denial of Service (DoS). By triggering the heap overflow, an attacker can cause the FFmpeg process or any application utilizing it to crash abruptly due to segmentation faults triggered by memory corruption detection mechanisms like glibc's malloc sanity checks. In environments where FFmpeg is used for real-time video processing, streaming services, or automated media conversion pipelines, such crashes can lead to significant service interruptions. If an attacker targets a server-side transcoder that processes uploaded videos from multiple users, they could potentially exhaust system resources by repeatedly crashing the worker processes, thereby preventing legitimate users from accessing video services. While heap overflows are often associated with arbitrary code execution through sophisticated exploitation techniques involving control flow hijacking, in this specific context, the immediate and most certain outcome is application termination and service disruption rather than full system compromise.
To mitigate this risk, it is imperative to apply the latest patches provided by FFmpeg maintainers, as commit 722a217 addresses these validation gaps by enforcing stricter bounds checking on input dimensions before memory allocation occurs. Organizations relying on FFmpeg should ensure their software stacks are updated to versions that include fixes for heap overflow vulnerabilities in libswscale. Additionally, deploying runtime protection mechanisms such as Address Space Layout Randomization (ASLR) and Data Execution Prevention (DEP) can reduce the likelihood of successful exploitation even if a vulnerability is present. For developers integrating FFmpeg into custom applications, implementing input sanitization at the application layer to validate video dimensions against reasonable maximums before passing them to library functions adds an extra layer of defense. Monitoring system logs for abnormal process terminations related to ffmpeg processes can also aid in detecting potential attempts to exploit this flaw in production environments.
This vulnerability aligns with ATT&CK technique T1499, Endpoint Denial of Service, as it involves leveraging a software weakness to disrupt the availability of a critical component within an endpoint or server infrastructure. The exploitation path typically falls under Initial Access via Spearphishing Attachment if delivered through malicious media files, followed by Execution leading to Impact on Availability. Security teams should prioritize patching this specific library version and review ingestion pipelines for any lack of input validation regarding multimedia file structures. Regular security audits focusing on memory safety in C/C++ based libraries remain essential given the persistent nature of buffer overflow vulnerabilities in legacy codebases that handle untrusted binary data formats.