CVE-2021-43256 [High] | RCE in 365 Apps

CVE-2021-43256 is rated Moderate Risk (58.3/100): CVSS High severity, with medium exploitation likelihood (EPSS 0.95%). Review affected assets and schedule remediation.

#	Date	Old EPSS score	New EPSS score	Delta (New - Old)
1	2026-05-08	0.61%	0.95%	+0.33%
2	2025-11-21	0.73%	0.61%	-0.12%
3	2025-11-18	—	0.73%	—

Date

Old EPSS score

New EPSS score

Delta (New - Old)

2026-05-08

0.61%

0.95%

+0.33%

2025-11-21

0.73%

0.61%

-0.12%

2025-11-18

—

0.73%

—

Base score	Version	Severity	Vector	Exploitability	Impact	Score source
7.8	3.1	HIGH	`CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H` Click to expand Attack vector (AV:L) They already need access on the box, or another person has to do something wrong; it’s not a remote drive-by. Attack complexity (AC:L) Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup. Privileges required (PR:N) No account or special rights needed—anonymous or random user is enough. User interaction (UI:R) A real person has to do something—click, install, enable—otherwise it doesn’t land. Scope (S:U) Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems. Confidentiality (C:H) Serious risk that confidential data gets exposed in a big way. Integrity (I:H) They could widely tamper with or forge data—trust in the data is badly hurt. Availability (A:H) Could take the service down hard or make it unusable for people who depend on it.	1.8	5.9	[email protected]
7.8	3.1	HIGH	`CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H` Click to expand Attack vector (AV:L) They already need access on the box, or another person has to do something wrong; it’s not a remote drive-by. Attack complexity (AC:L) Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup. Privileges required (PR:N) No account or special rights needed—anonymous or random user is enough. User interaction (UI:R) A real person has to do something—click, install, enable—otherwise it doesn’t land. Scope (S:U) Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems. Confidentiality (C:H) Serious risk that confidential data gets exposed in a big way. Integrity (I:H) They could widely tamper with or forge data—trust in the data is badly hurt. Availability (A:H) Could take the service down hard or make it unusable for people who depend on it.	1.8	5.9	[email protected]
6.8	2.0	MEDIUM	`AV:N/AC:M/Au:N/C:P/I:P/A:P` Click to expand Access vector (AV:N) Can be exploited remotely over network reachability. Access complexity (AC:M) Exploitation needs some favorable conditions, but not exceptional ones. Authentication (AU:N) No authentication is required. Confidentiality impact (C:P) Partial confidentiality impact. Integrity impact (I:P) Partial integrity impact. Availability impact (A:P) Partial availability impact.	8.6	6.4	[email protected]

Base score

Version

Severity

Vector

Exploitability

Impact

Score source

7.8

3.1

HIGH

CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H Click to expand

Attack vector (AV:L): They already need access on the box, or another person has to do something wrong; it’s not a remote drive-by.
Attack complexity (AC:L): Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N): No account or special rights needed—anonymous or random user is enough.
User interaction (UI:R): A real person has to do something—click, install, enable—otherwise it doesn’t land.
Scope (S:U): Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H): Serious risk that confidential data gets exposed in a big way.
Integrity (I:H): They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H): Could take the service down hard or make it unusable for people who depend on it.

1.8

5.9

[email protected]

7.8

3.1

HIGH

CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H Click to expand

Attack vector (AV:L): They already need access on the box, or another person has to do something wrong; it’s not a remote drive-by.
Attack complexity (AC:L): Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N): No account or special rights needed—anonymous or random user is enough.
User interaction (UI:R): A real person has to do something—click, install, enable—otherwise it doesn’t land.
Scope (S:U): Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H): Serious risk that confidential data gets exposed in a big way.
Integrity (I:H): They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H): Could take the service down hard or make it unusable for people who depend on it.

1.8

5.9

[email protected]

6.8

2.0

MEDIUM

AV:N/AC:M/Au:N/C:P/I:P/A:P Click to expand

Access vector (AV:N): Can be exploited remotely over network reachability.
Access complexity (AC:M): Exploitation needs some favorable conditions, but not exceptional ones.
Authentication (AU:N): No authentication is required.
Confidentiality impact (C:P): Partial confidentiality impact.
Integrity impact (I:P): Partial integrity impact.
Availability impact (A:P): Partial availability impact.

8.6

6.4

[email protected]

Affected software / configurations for CVE-2021-43256

Vendor	Product	Version	Raw CPE
microsoft	365_apps	—	cpe:2.3:a:microsoft:365_apps:-::::enterprise::x64:*
microsoft	365_apps	—	cpe:2.3:a:microsoft:365_apps:-::::enterprise::x86:*
microsoft	excel	2013	cpe:2.3:a:microsoft:excel:2013:sp1:::::x64:*
microsoft	excel	2013	cpe:2.3:a:microsoft:excel:2013:sp1:::::x86:*
microsoft	excel	2016	cpe:2.3:a:microsoft:excel:2016::::::x64:
microsoft	excel	2016	cpe:2.3:a:microsoft:excel:2016::::::x86:
microsoft	excel_rt	2013	cpe:2.3:a:microsoft:excel_rt:2013:sp1::::::
microsoft	office	2019	cpe:2.3:a:microsoft:office:2019::::::x64:
microsoft	office	2019	cpe:2.3:a:microsoft:office:2019::::::x86:
microsoft	office_long_term_servicing_channel	2021	cpe:2.3:a:microsoft:office_long_term_servicing_channel:2021::::::x64:
microsoft	office_long_term_servicing_channel	2021	cpe:2.3:a:microsoft:office_long_term_servicing_channel:2021::::::x86:
microsoft	office_online_server	—	cpe:2.3:a:microsoft:office_online_server:-:::::::*
microsoft	office_web_apps	2013	cpe:2.3:a:microsoft:office_web_apps:2013:sp1::::::

References for CVE-2021-43256

URL	Tags
https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-43256	Patch Vendor Advisory

URL

CVE-2021-43256 | Microsoft Excel Remote Code Execution Vulnerability

Exploit prediction scoring system (EPSS) score for CVE-2021-43256

Common vulnerability scoring system (CVSS) metrics for CVE-2021-43256

Weakness enumeration for CVE-2021-43256

GitHub Security Advisory for CVE-2021-43256

Affected software / configurations for CVE-2021-43256

References for CVE-2021-43256