---
id: "CVE-2026-125175"
page: "https://infrastack.ai/live/CVE-2026-125175"
kind: "vulnerability"
aliases: ["CVE-2026-125175"]
title: "FFmpeg: crafted FLV file leaks uninitialized heap memory into video output"
severity: "medium"
cvss: 4.8
epss: null
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["ffmpeg", "media-processing", "package", "self-hosted"]
not_affected_if: ["no-flv-decoding", "trusted-input-only"]
published_at: "2026-11-09T19:16:52+00:00"
first_seen_at: "2026-11-09T19:28:16+00:00"
updated_at: "2026-11-09T19:32:25+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-125175", "first_seen_at": "2026-11-09T19:28:16+00:00"}]
exploit_sources: []
---

# FFmpeg: crafted FLV file leaks uninitialized heap memory into video output

Link for people: https://infrastack.ai/live/CVE-2026-125175 (this .md is for agents)

FFmpeg's Flash Screen Video decoder copies uninitialized heap memory into decoded frames when zlib output is short. An attacker who supplies a crafted FLV file can recover heap contents from the decoded or re-encoded output.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- Check the installed FFmpeg version with `ffmpeg -version`; the sources say versions through 9.0.2 are affected.
- Look for FLV/FSV1 (Flash Screen Video) decoding in pipelines that process untrusted uploads.

## Fix

- FFmpeg patches are linked from the sources (github.com); fixed version numbers are unknown.

## Timeline

- 2026-11-09T19:28:16+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-125175

## Documents

- [advisory] Third-party advisory: www.vulncheck.com https://www.vulncheck.com/advisories/ffmpeg-through-9.0.2-information-disclosure-via-flash-screen-video-decoder
- [fix] Patch: github.com https://github.com/FFmpeg/FFmpeg/commit/50d206a75b5e60261d71b25657ae04891eb60290
- [fix] Patch: github.com https://github.com/FFmpeg/FFmpeg/commit/cfb40c912927fdd2c1186b7b6aca468422da23db

## From the sources

FFmpeg through 9.0.2 contains an information disclosure vulnerability in flashsv_decode_block() in libavcodec/flashsv.c that copies uninitialized heap memory into decoded frames when inflate output is short. Attackers can supply a crafted FLV with an FSV1 stream whose zlib block data decompresses short, then recover heap contents from the decoded or re-encoded output.

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