CVE-2021-3716

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LowLow ImpactWhat does this mean?

3.5CVSS v3 Score Breakdown

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Description

Statement

Mitigation

Additional information

Affected Packages

CVSS Score Details

Weakness (CWE)

Acknowledgements

FAQ

Description

A flaw was found in nbdkit due to to improperly caching plaintext state across the STARTTLS encryption boundary. A MitM attacker could use this flaw to inject a plaintext NBD_OPT_STRUCTURED_REPLY before proxying everything else a client sends to the server, potentially leading the client to terminate the NBD session. The highest threat from this vulnerability is to system availability.

Statement

Red Hat Enterprise Linux 7 is not affected by this flaw as it ships an old version of nbdkit (v1.8.0) that does not include support for NBD Structured Replies.

Mitigation

In general, it is recommended to use forced TLS (--tls=require) to avoid MitM attacks in the first place. If opportunistic encryption must be used (--tls=yes), ensure that clients that want to use TLS will request structured replies after the encryption is enabled. If this cannot be done, apply network filtering (e.g., firewall, TCP wrappers, etc.) or use a Unix domain socket instead of TCP to ensure that untrusted clients cannot connect to nbdkit as a MitM attacker.

Additional information

Bugzilla 1994695: nbdkit: NBD_OPT_STRUCTURED_REPLY injection on STARTTLS
CWE-924: Improper Enforcement of Message Integrity During Transmission in a Communication Channel
FAQ: Frequently asked questions about CVE-2021-3716

External references

https://www.cve.org/CVERecord?id=CVE-2021-3716

https://nvd.nist.gov/vuln/detail/CVE-2021-3716

https://listman.redhat.com/archives/libguestfs/2021-August/msg00083.html

https://www.openwall.com/lists/oss-security/2021/08/18/2

Common Vulnerability Scoring System (CVSS) Score Details

Important note

CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).

CVSS v3 Score Breakdown
	Red Hat	NVD
CVSS v3 Base Score	3.5	3.1
Attack Vector	Network	Network
Attack Complexity	Low	High
Privileges Required	Low	Low
User Interaction	Required	None
Scope	Unchanged	Unchanged
Confidentiality Impact	None	None
Integrity Impact	None	None
Availability Impact	Low	Low

CVSS v3 Vector

Red Hat: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:N/I:N/A:L

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

Understanding the Weakness (CWE)

CWE-924

Integrity,Confidentiality

Technical Impact: Gain Privileges or Assume Identity

If an attackers can spoof the endpoint, the attacker gains all the privileges that were intended for the original endpoint.

Acknowledgements

This issue was discovered by Eric Blake (Red Hat).

Frequently Asked Questions

Why is Red Hat's CVSS v3 score or Impact different from other vendors?

For open source software shipped by multiple vendors, the CVSS base scores may vary for each vendor's version depending on the version they ship, how they ship it, the platform, and even how the software is compiled. This makes scoring of vulnerabilities difficult for third-party vulnerability databases such as NVD that only provide a single CVSS base score for each vulnerability. Red Hat scores reflect how a vulnerability affects our products specifically.

For more information, see https://access.redhat.com/solutions/762393.

My product is listed as "Under investigation" or "Affected", when will Red Hat release a fix for this vulnerability?

"Under investigation" doesn't necessarily mean that the product is affected by this vulnerability. It only means that our Analysis Team is still working on determining whether the product is affected and how it is affected.
The term "Affected" means that our Analysis team has determined that this product, such as Red Hat Enterprise Linux 8 or OpenShift Container Platform 4, is affected by this vulnerability and a fix may be released to address this issue in the near future. This includes all minor releases of this product unless noted otherwise in the Statement text.

What can I do if my product is listed as "Will not fix"?

A "will not fix" status means that a fix for an affected product version is not planned or not possible due to complexity, which may create additional risk.

Available options depend mostly on the Impact of the vulnerability and the current Life Cycle phase of your product. Overall, you have the following options:

Upgrade to a supported product version that includes a fix for this vulnerability (recommended).
Apply a mitigation (if one exists).
Open a support case to request a prioritization of releasing a fix for this vulnerability.

What can I do if my product is listed as "Fix deferred"?

A deferred status means that a fix for an affected product version is not guaranteed due to higher-priority development work.

Available options depend mostly on the Impact of the vulnerability and the current Life Cycle phase of your product. Overall, you have the following options:

Apply a mitigation (if one exists).
Open a support case to request a prioritization of releasing a fix for this vulnerability.
Red Hat Engineering focuses on addressing high-priority issues based on their complexity or limited lifecycle support. Therefore, lower-priority issues will not receive immediate fixes.

What is a mitigation?

I have a Red Hat product but it is not in the above list, is it affected?

Why is my security scanner reporting my product as vulnerable to this vulnerability even though my product version is fixed or not affected?

In order to maintain code stability and compatibility, Red Hat usually does not rebase packages to entirely new versions. Instead, we backport fixes and new features to an older version of the package we distribute. This can result in some security scanners that only consider the package version to report the package as vulnerable. To avoid this, we suggest that you use an approved vulnerability scanner from our Red Hat Vulnerability Scanner Certification program.

My product is listed as "Out of Support Scope". What does this mean?

When a product is listed as "Out of Support Scope", it means a vulnerability with the impact level assigned to this CVE is no longer covered by its current support lifecycle phase. The product has been identified to contain the impacted component, but analysis to determine whether it is affected or not by this vulnerability was not performed. The product should be assumed to be affected. Customers are advised to apply any mitigation options documented on this page, consider removing or disabling the impacted component, or upgrade to a supported version of the product that has an update available.

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CVE-2021-3716

Insights vulnerability analysis

Description

Statement

Mitigation

Additional information

External references

Common Vulnerability Scoring System (CVSS) Score Details

Important note

CVSS v3 Vector

Understanding the Weakness (CWE)

Integrity,Confidentiality

Acknowledgements

Frequently Asked Questions

Why is Red Hat's CVSS v3 score or Impact different from other vendors?

My product is listed as "Under investigation" or "Affected", when will Red Hat release a fix for this vulnerability?

What can I do if my product is listed as "Will not fix"?

What can I do if my product is listed as "Fix deferred"?

What is a mitigation?

I have a Red Hat product but it is not in the above list, is it affected?

Why is my security scanner reporting my product as vulnerable to this vulnerability even though my product version is fixed or not affected?

My product is listed as "Out of Support Scope". What does this mean?

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