CVE-2021-40831 [Medium] | Spoofing in Amazon Web Services Aws-C-Io

The AWS IoT Device SDK v2 for Java, Python, C++ and Node.js appends a user supplied Certificate Authority (CA) to the root CAs instead of overriding it on macOS systems. Additionally, SNI validation is also not enabled when the CA has been “overridden”. TLS handshakes will thus succeed if the peer can be verified either from the user-supplied CA or the system’s default trust-store. Attackers with access to a host’s trust stores or are able to compromise a certificate authority already in the host's trust store (note: the attacker must also be able to spoof DNS in this case) may be able to use this issue to bypass CA pinning. An attacker could then spoof the MQTT broker, and either drop traffic and/or respond with the attacker's data, but they would not be able to forward this data on to the MQTT broker because the attacker would still need the user's private keys to authenticate against the MQTT broker. The 'aws_tls_ctx_options_override_default_trust_store_*' function within the aws-c-io submodule has been updated to address this behavior. This issue affects: Amazon Web Services AWS IoT Device SDK v2 for Java versions prior to 1.5.0 on macOS. Amazon Web Services AWS IoT Device SDK v2 for Python versions prior to 1.7.0 on macOS. Amazon Web Services AWS IoT Device SDK v2 for C++ versions prior to 1.14.0 on macOS. Amazon Web Services AWS IoT Device SDK v2 for Node.js versions prior to 1.6.0 on macOS. Amazon Web Services AWS-C-IO 0.10.7 on macOS.

#	Date	Old EPSS score	New EPSS score	Delta (New - Old)
1	2026-06-15	0.26%	0.61%	+0.35%
2	2025-03-30	0.51%	0.26%	-0.25%
3	2025-03-29	—	0.51%	—

Date

Old EPSS score

New EPSS score

Delta (New - Old)

2026-06-15

0.26%

0.61%

+0.35%

2025-03-30

0.51%

0.26%

-0.25%

2025-03-29

—

0.51%

—

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]
7.2	3.1	HIGH	`CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/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:H) They need powerful rights—admin, root, or similar—before this pays off. 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.	1.2	5.9	[email protected]
6.0	2.0	MEDIUM	`AV:N/AC:M/Au:S/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:S) A single authentication is required. Confidentiality impact (C:P) Partial confidentiality impact. Integrity impact (I:P) Partial integrity impact. Availability impact (A:P) Partial availability impact.	6.8	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]

7.2

3.1

HIGH

CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/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:H): They need powerful rights—admin, root, or similar—before this pays off.
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.

1.2

5.9

[email protected]

6.0

2.0

MEDIUM

AV:N/AC:M/Au:S/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:S): A single authentication is required.
Confidentiality impact (C:P): Partial confidentiality impact.
Integrity impact (I:P): Partial integrity impact.
Availability impact (A:P): Partial availability impact.

6.8

6.4

[email protected]

OS Trackers for CVE-2021-40831

vendor	priority	summary	link
`ubuntu`	medium	CVE-2021-40831 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, needs-triage 1.	https://ubuntu.com/security/CVE-2021-40831

Affected software / configurations for CVE-2021-40831

Vendor	Product	Version	Raw CPE
amazon	amazon_web_services_aws-c-io	0.10.7	cpe:2.3:a:amazon:amazon_web_services_aws-c-io:0.10.7:::::::*
amazon	amazon_web_services_internet_of_things_device_software_development_kit_v2	< 1.5.0	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	< 1.6.0	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	< 1.7.0	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	< 1.14.0	cpe:2.3:a:amazon:amazon_web_services_internet_of_things_device_software_development_kit_v2::::::c\+\+::*

References for CVE-2021-40831

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-2021-40831 | Missing SNI validation and inconsistent CA override function behavior within AWS IoT Device SDKs on Apple devices

Exploit prediction scoring system (EPSS) score for CVE-2021-40831

Common vulnerability scoring system (CVSS) metrics for CVE-2021-40831

Weakness enumeration for CVE-2021-40831

GitHub Security Advisory for CVE-2021-40831

OS Trackers for CVE-2021-40831

Affected software / configurations for CVE-2021-40831

References for CVE-2021-40831