Remote code execution in Microsoft Excel

1) Use-after-free

EUVDB-ID: #VU53912

Risk: High

CVSSv4.0: 7.3 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:P/U:Amber]

CVE-ID: CVE-2021-31939

CWE-ID: CWE-416 - Use After Free

Exploit availability: Yes

Description

The vulnerability allows a remote attacker to compromise vulnerable system.

The vulnerability exists due to a use-after-free error when processing Excel files. A remote attacker can create a specially crafted Excel file, trick the victim into opening it, trigger a use-after-free error and execute arbitrary code on the system.

Successful exploitation of the vulnerability may allow an attacker to compromise vulnerable system.

Mitigation

Install updates from vendor's website.

Vulnerable software versions

Office Online Server: 2016

Microsoft Office: 2013 RT - 2019

Microsoft Excel: 2013 RT Service Pack 1 - 2016

Microsoft Office Web Apps Server: 2013 Service Pack 1

CPE2.3

• cpe:2.3:a:microsoft:office_online_server:2016:*:*:*:*:*:*:*
• cpe:2.3:a:microsoft:microsoft_office:*:*:*:*:*:*:*:*
• cpe:2.3:a:microsoft:microsoft_excel:2013_RT_Service_Pack_1:*:*:*:*:microsoft_office:*:*
• cpe:2.3:a:microsoft:microsoft_excel:*:*:*:*:*:microsoft_office:*:*
• cpe:2.3:a:microsoft:microsoft_office_web_apps_server:2013 Service Pack 1:*:*:*:*:*:*:*

External links

https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-31939
https://www.zerodayinitiative.com/advisories/ZDI-21-670/

Q & A

Can this vulnerability be exploited remotely?

Yes. This vulnerability can be exploited by a remote non-authenticated attacker via the Internet.

Is there known malware, which exploits this vulnerability?

No. We are not aware of malware exploiting this vulnerability.