{"id":"CVE-2026-120246","kind":"vulnerability","aliases":["CVE-2026-120246"],"related":[],"title":"FFmpeg: CDXL decoder leaks stack memory into decoded video pixels","description":"FFmpeg 4.4 through 9.0.2 contains a use of uninitialized variable vulnerability in the CDXL decoder that leaks stack memory into decoded pixels via unfilled HAM palette entries. Attackers can craft a type-0 CDXL file whose HAM pixels select unfilled new_palette entries in cdxl_decode_ham8() or cdxl_decode_ham6(), exposing stack bytes and pointer fragments in the BGR24 output.","summary":"FFmpeg's CDXL decoder reads palette entries it never initialized when decoding HAM-encoded frames. A crafted CDXL file can make decoded output contain leftover stack bytes and pointer fragments, which can leak memory contents.","severity":"medium","cvss":6.8,"epss":null,"exploited":false,"exploited_at":null,"products":[],"ecosystems":[],"tags":["ffmpeg","media-processing","package","self-hosted"],"not_affected_if":["cdxl-not-used","no-untrusted-media"],"how_to_check":"- Run `ffmpeg -version` and compare against the affected range 4.4 through 9.0.2.\n- Check whether FFmpeg is built with the CDXL decoder enabled (`ffmpeg -decoders | grep cdxl`).","fix":null,"status":"open","published_at":"2026-11-01T01:17:18+00:00","first_seen_at":"2026-11-01T01:47:22+00:00","triaged_at":"2026-11-01T01:47:38+00:00","updated_at":"2026-11-01T01:47:38+00:00","category":"package","confidence":0.6,"triage":{"at":"2026-11-01T01:47:38Z","model":"claude-haiku-5-5","output":{"fix":"unknown","reach":"unknown","title":"FFmpeg: CDXL decoder leaks stack memory into decoded video pixels","impact":"low","summary":"FFmpeg's CDXL decoder reads palette entries it never initialized when decoding HAM-encoded frames. A crafted CDXL file can make decoded output contain leftover stack bytes and pointer fragments, which can leak memory contents.","audience":"businesses","category":"package","nicknames":[],"who_cares":["ffmpeg","media-processing","self-hosted"],"confidence":0.6,"fix_status":"unknown","needs_auth":"no","worst_case":"Stack memory fragments leak into decoded output images","analyst_note":"Confirm the fixed FFmpeg version and whether a patch exists, using the NVD entry https://nvd.nist.gov/vuln/detail/CVE-2026-120246 and upstream FFmpeg commits.","how_to_check":"- Run `ffmpeg -version` and compare against the affected range 4.4 through 9.0.2.\n- Check whether FFmpeg is built with the CDXL decoder enabled (`ffmpeg -decoders | grep cdxl`).\n- unknown for whether your own workloads decode untrusted CDXL input.","plain_action":"","needs_analyst":true,"not_affected_if":["no-untrusted-media","cdxl-not-used"],"who_is_affected":"Systems that run FFmpeg 4.4 through 9.0.2 to decode CDXL files, especially services that accept user-uploaded media and convert it. Deployments that never decode CDXL input or only process trusted files are less exposed. The sources do not name a patched version.","user_interaction":"unknown","needs_special_setup":"no","severity_if_unknown":"medium"},"cost_usd":0.000728,"input_tokens":4200,"output_tokens":617,"severity_before":"medium"},"analyst_status":null,"analyst_note":null,"search":"'-0':93C '-120246':13A,16A '-2026':12A,15A '4.4':62C '9.0.2':64C 'attack':88C 'bgr24':120C 'byte':52B,114C 'cdxl':2A,27B,43B,74C,94C,105C,109C 'contain':49B,65C 'content':60B 'craft':42B,90C 'cve':11A,14A 'decod':3A,8A,28B,36B,47B,75C,81C,106C,110C 'encod':39B 'entri':31B,87C,103C 'expos':112C 'ffmpeg':1A,17B,25B,61C 'file':44B,95C 'fragment':55B,117C 'frame':40B 'ham':38B,85C,97C 'ham-encod':37B 'ham6':111C 'ham8':107C 'host':24B 'initi':34B 'leak':4A,58B,77C 'leftov':50B 'make':46B 'media':19B 'media-process':18B 'memori':6A,59B,79C 'never':33B 'new':101C 'output':48B,121C 'packag':21B 'palett':30B,86C,102C 'pixel':10A,82C,98C 'pointer':54B,116C 'process':20B 'read':29B 'select':99C 'self':23B 'self-host':22B 'stack':5A,51B,78C,113C 'type':92C 'unfil':84C,100C 'uniniti':69C 'use':67C 'variabl':70C 'via':83C 'video':9A 'vulner':71C 'whose':96C","nicknames":[],"mitigations":[],"who_affected":"Systems that run FFmpeg 4.4 through 9.0.2 to decode CDXL files, especially services that accept user-uploaded media and convert it. Deployments that never decode CDXL input or only process trusted files are less exposed. The sources do not name a patched version.","tier":"C","verified":{},"analyst_revisit_at":null,"fix_status":"none","audience":"businesses","plain_action":null,"first_public_at":"2026-11-01T01:17:18+00:00","kev":null,"cvss_vector":"CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:P/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X","cvss_by":"disclosure@vulncheck.com","poc_count":0,"sources":[{"source":"nvd","external_id":"CVE-2026-120246","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-120246","severity":null,"published_at":"2026-11-01T01:17:18+00:00","modified_at":"2026-11-01T01:17:18+00:00","first_seen_at":"2026-11-01T01:47:22+00:00","fetched_at":"2026-11-01T01:47:22+00:00","note":null}],"documents":[],"notice":"Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai"}