CVE-2021-3716

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Last Modified: UTC

Low Low Impact What does this mean?
3.5 CVSS v3 Base Score

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

External References

Content from www.cve.org is not included.https://www.cve.org/CVERecord?id=CVE-2021-3716

Content from nvd.nist.gov is not included.https://nvd.nist.gov/vuln/detail/CVE-2021-3716

This content is not included.https://listman.redhat.com/archives/libguestfs/2021-August/msg00083.html

Content from www.openwall.com is not included.https://www.openwall.com/lists/oss-security/2021/08/18/2

Affected Packages and Issued Red Hat Security Errata

Products / Services Components State Errata
Advanced Virtualization for RHEL 8.5.0.Z virt-devel:av Fixed RHSA-2022:0397
Advanced Virtualization for RHEL 8.5.0.Z virt:av Fixed RHSA-2022:0397
Red Hat Enterprise Linux 7 nbdkit Not affected
Red Hat Enterprise Linux 8 virt-devel:rhel Fixed RHSA-2022:1759
Red Hat Enterprise Linux 8 virt:rhel Fixed RHSA-2022:1759
Red Hat Enterprise Linux 8 Advanced Virtualization virt:av/nbdkit Affected
Red Hat Enterprise Linux 8 Advanced Virtualization virt:8.2/nbdkit Fix deferred
Red Hat Enterprise Linux 8 Advanced Virtualization virt:8.3/nbdkit Out of support scope
Red Hat Enterprise Linux 9 nbdkit Not affected
Red Hat Virtualization 4 nbdkit Not affected
Unless explicitly stated as not affected, all previous versions of packages in any minor update stream of a product listed here should be assumed vulnerable, although may not have been subject to full analysis.

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 Authorities (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

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.
  • "Affected" means that our Analysis Team has determined that this product is affected by this vulnerability and might release a fix to address this in the near future.

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 This content is not included.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 This content is not included.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?

 A mitigation is an action that can be taken to reduce the impact of a security vulnerability, without deploying any fixes.

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

 The listed products were found to include one or more of the components that this vulnerability affects. These products underwent a thorough evaluation to determine their affectedness by this vulnerability. Note that layered products (such as container-based offerings) that consume affected components from any of the products listed in this table may be affected and are not represented.

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 This content is not included.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.