Microsoft waarschuwt Office-gebruikers voor een bug die CVE-2021-40444 wordt genoemd. De bug wordt omschreven als de ‘Microsoft MSHTML Remote Code Execution Vulnerability’.
De bug heeft nog geen patch, dus het is wat bekend staat als een zero-day, steno voor “de ethische hackers waren de niet-ethische hackers nul dagen voor met een patch voor deze kwetsbaarheid”. De kwetsbaarheid is ontdekt door EXPMON en Mandiant.
💥💥⚡️⚡️
— EXPMON (@EXPMON_) September 7, 2021
EXPMON system detected a highly sophisticated #ZERO-DAY ATTACK ITW targeting #Microsoft #Office users! At this moment, since there's no patch, we strongly recommend that Office users be extremely cautious about Office files – DO NOT OPEN if not fully trust the source!
Voor zover we weten werkt de kwetsbaarheid op de volgende manier:
MSHTML is geen volwaardige browser, zoals Internet Explorer of Edge, maar is een onderdeel van het besturingssysteem dat kan worden gebruikt om browsers of browser-achtige toepassingen te maken die HTML-bestanden moeten of willen weergeven.
Hoewel HTML het meest wordt geassocieerd met surfen op het web, vinden veel andere toepassingen dan browsers het nuttig om web inhoud te kunnen renderen en weergeven, bijvoorbeeld als een handige en goed uitziende manier om documentatie en bestanden te presenteren.
“HTML is niet alleen voor browsen”
Dit betekent dat bugs in HTML-rendering niet alleen van invloed zijn op uw browser en uw browseactiviteiten. Cybercriminelen kunnen niet alleen een onbetrouwbare weblink naar u sturen, maar ook een misleiding creëren in onbetrouwbare code voor webrendering, en zo kunnen ze zoeken naar exploits.
Zelfs als er een bug is die ze niet goed genoeg kunnen controleren, kunnen de cybercrimenelen in staat zijn om andere applicaties te vinden waarbij de kwetsbaarheid niet alleen kan worden gebruikt om de app te laten crashen, maar ook om de app te misbruiken om de controle over te nemen en malware te implanteren.
Dat is wat CVE-2021-40444 lijkt te doen, waarbij de aanval wordt uitgevoerd via Office-bestanden die in Word, Excel enzovoort worden geladen, in plaats van via webpagina’s die rechtstreeks in de browser worden bekeken.
Hou de patch van Microsoft in de gaten. Volgende week dinsdag (09-14-2021) is de september ’21 Patch Tuesday.
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