CVE-2021-40831Network attack vector

MQTT broker spoofing via incomplete CA override

Published Nov 22, 2021 · Updated Aug 4, 2024

Improper certificate validation in AWS IoT Device SDK v2 and AWS-C-IO on macOS allows attackers to spoof an MQTT broker. The aws_tls_ctx_options_override_default_trust_store_* functions append a supplied CA to system roots and omit SNI validation instead of replacing the default trust store. Exploitation requires trust-store access or a compromised trusted CA plus DNS spoofing; attackers can drop traffic or return false broker data but cannot relay it without the device private key.

CVSS severity7.3
High
EPSS probability0.64%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper certificate validation in AWS IoT Device SDK v2 and AWS-C-IO on macOS allows attackers to spoof an MQTT broker. The aws_tls_ctx_options_override_default_trust_store_* functions append a supplied CA to system roots and omit SNI validation instead of replacing the default trust store. Exploitation requires trust-store access or a compromised trusted CA plus DNS spoofing; attackers can drop traffic or return false broker data but cannot relay it without the device private key.

The record

CVE
CVE-2021-40831
Published
Nov 22, 2021
Updated
Aug 4, 2024
Vendor
Amazon Web Services
Product
AWS IoT Device SDK v2 for Python
Classifications
CWE-295, T1557
Attack vector
network
Privileges
admin

Timeline

How it unfolded

  1. Nov 22, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=unspecified <1.7.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesadmin

What is affected?

Amazon Web Services · AWS IoT Device SDK v2 for Pythonversion=unspecified <1.7.0
Amazon Web Services · AWS IoT Device SDK v2 for C++version=unspecified <1.14.0
Amazon Web Services · AWS-C-IOversion=0.10.7
Amazon Web Services · AWS IoT Device SDK v2 for Javaversion=unspecified <1.5.0
Amazon Web Services · AWS IoT Device SDK v2 for Node.jsversion=unspecified <1.6.0

Published CVSS scores

6.3OSVCVSS:3.1/AV:A/AC:H/PR:H/UI:R/S:U/C:H/I:H/A:H
7.3GitHub Advisory DatabaseCVSS:4.0/AV:N/AC:L/AT:P/PR:H/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesadmin
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-295Improper Certificate Validation
T1557Adversary-in-the-Middle

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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