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What is CVE-2021-40831?A high-severity flaw in Amazon Web Services Aws-C-Io, explained.

High severity3 affected products
The short answer

CVE-2021-40831 is a high-severity flaw (CVSS 7.2) in Amazon Web Services Aws-C-Io, published on 23 November 2021. It is not on the list of flaws known to be exploited today. The latest forecast puts its chance of use in the next 30 days at 0.6%. If you run an affected version, plan in the vendor’s fix.

Check if it affects you →How to fix it

Published 23 November 2021. Record last updated 2 December 2021. We keep this page's data up to date.

What it does

What is CVE-2021-40831? In plain terms.

It can be attacked from anywhere on the internet with an administrator account, and nobody has to click anything. If it works, the attacker can read data, change data and take it offline.

The official description

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.

What kind of flaw is it?

  • CWE-295Improper Certificate Validation
CVSS 3.1 scoreHigh · 7.2

How an attack on it works

Read straight from its severity rating, translated out of the shorthand.

  • Where an attacker can beAnywhere on the internet
  • How hard it is to pull offEasy: no special conditions
  • Login needed firstAn administrator account
  • Does someone have to clickNo, nobody has to do anything
  • What an attacker getsCan read data, change data and take it offline

Severity vector: CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H

Exploitation

Is CVE-2021-40831 being exploited? Not that we know of.

It is not on the list of flaws known to be exploited today. The latest forecast puts the chance of it being used in the next 30 days at 0.6%. That can change at any time, which is why we keep watching.

Known to be exploitedNoNot on the list of exploited flaws today
Chance of use in the next 30 days0.6%Its EPSS score, from the latest forecast

Timeline

  1. Published
  2. Record last updated
How EdgeProtect ranks it
46out of 100Medium

CVE-2021-40831 scores 46. Action: Plan remediation.

We keep the score of every published flaw up to date as the evidence changes. Four things go into the score, and evidence that criminals are actually using it counts most. In order:

  • Evidence it is being exploitedBiggest factor
  • How severe it isStrong factor
  • How widely exposed it isKey context
  • Real threat activity around itKey context

85 and above is Critical. Anything confirmed as exploited is always marked for an emergency patch, whatever its score.

When CVE-2021-40831 matches software you track, it lands in your list with its score and the reasons behind it.

See your own ranked list →
Affected products

Who is affected by CVE-2021-40831? 3 products.

The published record lists 3 products from 2 vendors. Versions are shown as published: "before 1.5.0" means every version up to, but not including, 1.5.0. If you run one of these, check your version, then go to the fix below.

Remediation

How do I fix CVE-2021-40831? Four steps.

  1. Check whether you run itCompare your versions with the affected products above. Not sure what you run? EdgeProtect can work it out from your public website, or you can pick it from a list.
  2. Apply the vendor’s fixInstall the latest update from the vendor. The references list where the vendor has published details.
  3. If you can’t patch todayFollow any mitigation the vendor publishes, and limit who can reach the affected system from the internet until the update is in.
  4. Keep an eye on itTrack the product and we tell you as soon as we spot this flaw on the list of exploited flaws, or a jump in its exploit likelihood.

References

5 links
EdgeProtect

Does CVE-2021-40831 affect you? We'll keep checking.

Looking flaws up one at a time doesn't scale. Tell us what you run once, and we tell you which flaws matter to you, in what order, and keep watching for new ones.

  1. Tell us what you runPick your software from a list, or let us work it out from your website.
  2. We match it to every flawOver 400,000 published flaws, checked against your list.
  3. Ranked by real-world riskA 0 to 100 score, led by evidence criminals are using it.
  4. Told as soon as we knowAn alert by email, in the app or by webhook to your own tools.
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FAQ

Common questions, answered plainly.

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CVE-2021-40831 is a high-severity flaw in Amazon Web Services Aws-C-Io, published on 23 November 2021. It can be attacked from anywhere on the internet with an administrator account, and nobody has to click anything. If it works, the attacker can read data, change data and take it offline.

It scores 7.2 out of 10 on the CVSS severity scale, which is high. Our risk score for CVE-2021-40831 is 46 out of 100, which is Medium. Its action is "Plan remediation". No sign of exploitation and a low forecast. Patch it in your normal update cycle.

It is not on the list of flaws known to be exploited today. The latest forecast puts the chance of it being used in the next 30 days at 0.6%. That can change at any time, which is why we keep watching.

For Amazon Web Services Aws-C-Io: 0.10.7. The record lists 3 products in all, each with its versions, under "Who is affected" on this page.

Install the update the vendor names in its advisory. If you can't patch today, follow the vendor's mitigation and limit who can reach the affected system from the internet.

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