CVE-2021-43527

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Last Modified: UTC

Critical Critical Impact What does this mean?
9.8 CVSS v3 Base Score

Description

A remote code execution flaw was found in the way NSS verifies certificates. This flaw allows an attacker posing as an SSL/TLS server to trigger this issue in a client application compiled with NSS when it tries to initiate an SSL/TLS connection. Similarly, a server application compiled with NSS, which processes client certificates, can receive a malicious certificate via a client, triggering the flaw. The highest threat to this vulnerability is confidentiality, integrity, as well as system availability.

Statement

The issue is not limited to TLS. Any applications that use NSS certificate verification are vulnerable; S/MIME is impacted as well. Similarly, a server application compiled with NSS, which processes client certificates, can receive a malicious certificate via a client.

Firefox is not vulnerable to this flaw as it uses the mozilla::pkix for certificate verification. Thunderbird is affected when parsing email with the S/MIME signature. Thunderbird on Red Hat Enterprise Linux 8.4 and later does not need to be updated since it uses the system NSS library, but earlier Red Hat Enterprise Linux 8 extended life streams will need to update Thunderbird as well as NSS.

Mitigation

Red Hat has investigated whether a possible mitigation exists for this issue, and has not been able to identify a practical example. Please update the affected package as soon as possible.

Additional Information

External References

Content from www.cve.org is not included.https://www.cve.org/CVERecord?id=CVE-2021-43527

Content from nvd.nist.gov is not included.https://nvd.nist.gov/vuln/detail/CVE-2021-43527

Content from googleprojectzero.blogspot.com is not included.https://googleprojectzero.blogspot.com/2021/12/this-shouldnt-have-happened.html

Content from www.mozilla.org is not included.https://www.mozilla.org/en-US/security/advisories/mfsa2021-51/

Affected Packages and Issued Red Hat Security Errata

Products / Services Components State Errata
Red Hat Enterprise Linux 6 thunderbird Not affected
Red Hat Enterprise Linux 6 Extended Lifecycle Support nss Fixed RHSA-2021:4907
Red Hat Enterprise Linux 7 nss Fixed RHSA-2021:4904
Red Hat Enterprise Linux 7 firefox Not affected
Red Hat Enterprise Linux 7 thunderbird Not affected
Red Hat Enterprise Linux 7.3 Advanced Update Support nss Fixed RHSA-2021:4994
Red Hat Enterprise Linux 7.4 Advanced Update Support nss Fixed RHSA-2021:4932
Red Hat Enterprise Linux 7.6 Advanced Update Support(Disable again in 2026 - SPRHEL-7118) nss Fixed RHSA-2021:4933
Red Hat Enterprise Linux 7.6 Telco Extended Update Support nss Fixed RHSA-2021:4933
Red Hat Enterprise Linux 7.6 Update Services for SAP Solutions nss Fixed RHSA-2021:4933
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 9.8 9.8
Attack Vector Network Network
Attack Complexity Low Low
Privileges Required None None
User Interaction None None
Scope Unchanged Unchanged
Confidentiality Impact High High
Integrity Impact High High
Availability Impact High High

CVSS v3 Vector

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

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

Acknowledgements

Red Hat would like to thank Tavis Ormandy (Project Zero) for reporting this issue. Upstream acknowledges the Mozilla project as the original reporter.

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.