According TrendMicro and Symantec this is a zero-day.
Backdoors Emdivi, Korplug and ZXshell were used in the cyberespionage campaign,тАЬOperation CloudyOmega,тАЭ to target Japanese organisations.
Vulnerable component: Ichitaro
CVSSv3 score: CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H/E:F/RL:O/RC:C
CWE-ID: CWE-119 - Improper Restriction of Operations within the Bounds of a Memory Buffer
The vulnerability allows a remote attacker to execute arbitrary code on the target system.
The weakness exists due to buffer overflow when processing documents. A remote attacker can create a specially crafted file, trick the victim into opening it, trigger memory corruption and execute arbitrary code with privileges of the current user.
Successful exploitation of the vulnerability results in arbitrary code execution on the vulnerable system.
Note: the vulnerability was being actively exploited.
Known APT campaigns:
The first attack traces back to at least 2011. The hackers used Backdoor.Emdivi to target mainly Japanese companies.