CVE-2021-33603 [Medium] | Denial of Service in Atlant

A Denial-of-Service (DoS) vulnerability was discovered in F-Secure Atlant whereby the AVPACK module component used in certain F-Secure products can crash while scanning a fuzzed files. The exploit can be triggered remotely by an attacker. A successful attack will result in Denial-of-Service (DoS) of the Anti-Virus engine.

#	Date	Old EPSS score	New EPSS score	Delta (New - Old)
1	2026-03-02	0.34%	0.23%	-0.11%
2	2025-03-30	0.53%	0.34%	-0.19%
3	2025-03-29	—	0.53%	—

Date

Old EPSS score

New EPSS score

Delta (New - Old)

2026-03-02

0.34%

0.23%

-0.11%

2025-03-30

0.53%

0.34%

-0.19%

2025-03-29

—

0.53%

—

Base score	Version	Severity	Vector	Exploitability	Impact	Score source
5.5	3.1	MEDIUM	`CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:L/I:L/A:L` Click to expand Attack vector (AV:N) Could be attacked over the internet or any normal routed network—not just someone sitting at the machine. 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:L) A normal user session is enough; they don’t have to be admin. 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:L) Some sensitive info could get out, but not a total data dump. Integrity (I:L) Attackers could change some data, but it’s limited—not everything goes. Availability (A:L) Might cause slowdowns, glitches, or partial disruption—not a full brick.	2.1	3.4	[email protected]
6.5	3.1	MEDIUM	`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H` Click to expand Attack vector (AV:N) Could be attacked over the internet or any normal routed network—not just someone sitting at the machine. 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:N) Doesn’t really leak secrets in a meaningful way. Integrity (I:N) Data isn’t meaningfully altered or forged. Availability (A:H) Could take the service down hard or make it unusable for people who depend on it.	2.8	3.6	[email protected]
4.3	2.0	MEDIUM	`AV:N/AC:M/Au:N/C:N/I:N/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:N) No confidentiality impact. Integrity impact (I:N) No integrity impact. Availability impact (A:P) Partial availability impact.	8.6	2.9	[email protected]

Base score

Version

Severity

Vector

Exploitability

Impact

Score source

5.5

3.1

MEDIUM

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

Attack vector (AV:N): Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
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:L): A normal user session is enough; they don’t have to be admin.
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:L): Some sensitive info could get out, but not a total data dump.
Integrity (I:L): Attackers could change some data, but it’s limited—not everything goes.
Availability (A:L): Might cause slowdowns, glitches, or partial disruption—not a full brick.

2.1

3.4

[email protected]

6.5

3.1

MEDIUM

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

Attack vector (AV:N): Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
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:N): Doesn’t really leak secrets in a meaningful way.
Integrity (I:N): Data isn’t meaningfully altered or forged.
Availability (A:H): Could take the service down hard or make it unusable for people who depend on it.

2.8

3.6

[email protected]

4.3

2.0

MEDIUM

AV:N/AC:M/Au:N/C:N/I:N/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:N): No confidentiality impact.
Integrity impact (I:N): No integrity impact.
Availability impact (A:P): Partial availability impact.

8.6

2.9

[email protected]

Affected software / configurations for CVE-2021-33603

Vendor	Product	Version	Raw CPE
f-secure	atlant	—	cpe:2.3:a:f-secure:atlant:-:::::::*
f-secure	cloud_protection_for_salesforce	—	cpe:2.3:a:f-secure:cloud_protection_for_salesforce:-:::::::*
f-secure	elements_for_microsoft_365	—	cpe:2.3:a:f-secure:elements_for_microsoft_365:-:::::::*
f-secure	internet_gatekeeper	—	cpe:2.3:a:f-secure:internet_gatekeeper:-:::::-::
f-secure	linux_security	—	cpe:2.3:a:f-secure:linux_security:-:::::::*
f-secure	elements_endpoint_detection_and_response	—	cpe:2.3:a:f-secure:elements_endpoint_detection_and_response:-:::::::*
f-secure	elements_endpoint_protection	—	cpe:2.3:a:f-secure:elements_endpoint_protection:-:::::::*

References for CVE-2021-33603

URL	Tags
https://www.f-secure.com/en/business/programs/vulnerability-reward-program/hall-of-fame	Vendor Advisory
https://www.f-secure.com/en/business/support-and-downloads/security-advisories/cve-2021-33603	Vendor Advisory

URL

CVE-2021-33603 | Denial-of-Service (DoS) Vulnerability

Exploit prediction scoring system (EPSS) score for CVE-2021-33603

Common vulnerability scoring system (CVSS) metrics for CVE-2021-33603

Weakness enumeration for CVE-2021-33603

Affected software / configurations for CVE-2021-33603

References for CVE-2021-33603