A Microsoft Office 0-day vulnerability that was disclosed just days ago is already being exploited by attackers associated with malware families such as Latentbot and WingBird.
Tracked as CVE-2017-0199, the security bug allows a malicious actor to craft a RTF (Rich Text Format) document that would download and execute a Visual Basic script containing PowerShell commands. Microsoft has already addressed the flaw, but not quick enough to prevent malware such as the Dridex banking Trojan from abusing it in attacks.
The exploit for this vulnerability was found to bypass most mitigations available before a patch was released, and could also render Protected View useless, security researchers discovered. This means that attacks leveraging the vulnerability don’t require user interaction to be successful.
The exploit leverages Office’s Object Linking and Embedding (OLE) functionality to link to an HTA (HTML Application) file hosted on a remote server. When the user opens the RTF document received via spam email, winword.exe issues a HTTP request to retrieve the malicious HTA file, which loads and executes the malicious Visual Basic script. In turn, the script downloads and executes malware.
According to FireEye, the malicious scripts used in these incidents were also observed terminating the winword.exe processes (to hide a prompt from OLE2link) and loading decoy documents.
The security researchers stumbled upon such attacks designed to distribute a newer variant of Latentbot, a highly obfuscated bot that has been active since 2013. The bot has a highly modular plugin architecture and has been also associated with the Pony infostealer.
Latentbot packs different injection mechanisms for Windows XP (x86) and Windows 7 operating systems: it uses Attrib.exe patching and Svchost code Injection on the former, but injects code into svchost.exe directly on the latter.
Another attack abusing this vulnerability consisted of two malicious stages, and distributed a variant of the dropper known as WingBird (which has similar characteristics as FinFisher). Heavily obfuscated, the malware packs several anti-analysis measures, including a custom VM to slow analysis, and was recently associated with the activities of a threat group known as NEODYMIUM.
Netskope Threat Research Labs, on the other hand, say that this Office zero-day vulnerability can also be linked to the Godzilla botnet loader. The researchers observed that the IPs related to the loader were serving payloads associated with exploits for this bug, but say that they “cannot speculate that the spam campaign and zero-day are related,” although the same attack group appears to be behind the attacks.
Office users are advised to apply the newly released patches as soon as possible, to ensure they are protected from these attacks.
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