CVE-2021-40828 [Medium] | Security Vulnerability in Amazon Web Services Aws-C-Io

Connections initialized by the AWS IoT Device SDK v2 for Java (versions prior to 1.3.3), Python (versions prior to 1.5.18), C++ (versions prior to 1.12.7) and Node.js (versions prior to 1.5.1) did not verify server certificate hostname during TLS handshake when overriding Certificate Authorities (CA) in their trust stores on Windows. This issue has been addressed in aws-c-io submodule versions 0.9.13 onward. This issue affects: Amazon Web Services AWS IoT Device SDK v2 for Java versions prior to 1.3.3 on Microsoft Windows. Amazon Web Services AWS IoT Device SDK v2 for Python versions prior to 1.5.18 on Microsoft Windows. Amazon Web Services AWS IoT Device SDK v2 for C++ versions prior to 1.12.7 on Microsoft Windows. Amazon Web Services AWS IoT Device SDK v2 for Node.js versions prior to 1.5.3 on Microsoft Windows.

#	Date	Old EPSS score	New EPSS score	Delta (New - Old)
1	2026-06-15	0.10%	0.40%	+0.30%
2	2025-03-30	0.26%	0.10%	-0.15%
3	2025-03-29	—	0.26%	—

Date

Old EPSS score

New EPSS score

Delta (New - Old)

2026-06-15

0.10%

0.40%

+0.30%

2025-03-30

0.26%

0.10%

-0.15%

2025-03-29

—

0.26%

—

Base score	Version	Severity	Vector	Exploitability	Impact	Score source
6.3	3.1	MEDIUM	`CVSS:3.1/AV:A/AC:H/PR:H/UI:R/S:U/C:H/I:H/A:H` Click to expand Attack vector (AV:A) Attacker has to be nearby on the network—same office, same link, that vibe—not the whole wide internet. Attack complexity (AC:H) Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work. Privileges required (PR:H) They need powerful rights—admin, root, or similar—before this pays off. 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.	0.4	5.9	[email protected]
8.8	3.1	HIGH	`CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H` Click to expand Attack vector (AV:A) Attacker has to be nearby on the network—same office, same link, that vibe—not the whole wide internet. 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:N) Nobody has to click “OK” or open a trap file; it can work without a victim helping. 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.	2.8	5.9	[email protected]
5.8	2.0	MEDIUM	`AV:A/AC:L/Au:N/C:P/I:P/A:P` Click to expand Access vector (AV:A) Requires access to an adjacent network segment. Access complexity (AC:L) Exploitation conditions are straightforward and predictable. 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.	6.5	6.4	[email protected]

Base score

Version

Severity

Vector

Exploitability

Impact

Score source

6.3

3.1

MEDIUM

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

Attack vector (AV:A): Attacker has to be nearby on the network—same office, same link, that vibe—not the whole wide internet.
Attack complexity (AC:H): Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work.
Privileges required (PR:H): They need powerful rights—admin, root, or similar—before this pays off.
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.

0.4

5.9

[email protected]

8.8

3.1

HIGH

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

Attack vector (AV:A): Attacker has to be nearby on the network—same office, same link, that vibe—not the whole wide internet.
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:N): Nobody has to click “OK” or open a trap file; it can work without a victim helping.
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.

2.8

5.9

[email protected]

5.8

2.0

MEDIUM

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

Access vector (AV:A): Requires access to an adjacent network segment.
Access complexity (AC:L): Exploitation conditions are straightforward and predictable.
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.

6.5

6.4

[email protected]

OS Trackers for CVE-2021-40828

vendor	priority	summary	link
`ubuntu`	medium	CVE-2021-40828 medium priority: Ubuntu including 1 source packages (aws-c-io), 7 status rows across 7 suites (bionic, focal, jammy, kinetic, trusty, upstream, xenial): DNE 4, ignored 2, released 1.	https://ubuntu.com/security/CVE-2021-40828

Affected software / configurations for CVE-2021-40828

Vendor	Product	Version	Raw CPE
amazon	amazon_web_services_aws-c-io	< 0.9.13	cpe:2.3:a:amazon:amazon_web_services_aws-c-io::::::::
amazon	amazon_web_services_internet_of_things_device_software_development_kit_v2	< 1.3.3	cpe:2.3:a:amazon:amazon_web_services_internet_of_things_device_software_development_kit_v2::::::java::*
amazon	amazon_web_services_internet_of_things_device_software_development_kit_v2	< 1.5.1	cpe:2.3:a:amazon:amazon_web_services_internet_of_things_device_software_development_kit_v2::::::node.js::*
amazon	amazon_web_services_internet_of_things_device_software_development_kit_v2	< 1.5.18	cpe:2.3:a:amazon:amazon_web_services_internet_of_things_device_software_development_kit_v2::::::python::*
amazon	amazon_web_services_internet_of_things_device_software_development_kit_v2	< 1.12.7	cpe:2.3:a:amazon:amazon_web_services_internet_of_things_device_software_development_kit_v2::::::c\+\+::*

References for CVE-2021-40828

URL	Tags
https://github.com/aws/aws-iot-device-sdk-cpp-v2	Product
https://github.com/aws/aws-iot-device-sdk-java-v2	Product
https://github.com/aws/aws-iot-device-sdk-js-v2	Product
https://github.com/aws/aws-iot-device-sdk-python-v2	Product
https://github.com/awslabs/aws-c-io/	Product

URL

CVE-2021-40828 | TLS hostname validation issues within AWS IoT Device SDKs on Windows

Exploit prediction scoring system (EPSS) score for CVE-2021-40828

Common vulnerability scoring system (CVSS) metrics for CVE-2021-40828

Weakness enumeration for CVE-2021-40828

GitHub Security Advisory for CVE-2021-40828

OS Trackers for CVE-2021-40828

Affected software / configurations for CVE-2021-40828

References for CVE-2021-40828