CA certificate check bypass with X509_V_FLAG_X509_STRICT
CVE: CVE-2021-3450
Component: openssl
CWE: CWE-295
Severity: Important
CVSS v3: 7.4/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
Release date: 2021-03-25T00:00:00+00:00

A flaw was found in openssl. The flag that enables additional security checks of certificates present in a certificate chain was not enabled allowing a confirmation step to verify that certificates in the chain are valid CA certificates is bypassed. The highest threat from this vulnerability is to data confidentiality and integrity.

Statement: This flaw affects openssl  1.1.1h  and above only, older versions are not affected by this flaw.

Remediation:
Before applying this update, make sure all previously released errata
relevant to your system have been applied.

For details on how to apply this update, refer to:

https://access.redhat.com/articles/11258
Before applying this update, make sure all previously released errata relevant to your system have been applied.

For details on how to apply this update, refer to:

https://access.redhat.com/articles/11258
Before applying this update, make sure all previously released errata
relevant to your system have been applied.

For details on how to apply this update, refer to:

https://access.redhat.com/articles/11258
For details on how to apply this update, which includes the changes described in this advisory, refer to:

https://access.redhat.com/articles/2974891

The system must be rebooted for this update to take effect. For the update to take effect, all services linked to the glibc library must be restarted, or the system rebooted.
For details on how to apply this update, which includes the changes described in this advisory, refer to:

https://access.redhat.com/articles/11258

For the update to take effect, all services linked to the OpenSSL library must be restarted, or the system rebooted.
Before applying the update, back up your existing installation, including all applications, configuration files, databases and database settings, and so on.

The References section of this erratum contains a download link for the update. You must be logged in to download the update.
Before applying the update, back up your existing installation, including all applications, configuration files, databases and database settings, and so on.

The References section of this erratum contains a download link for the update. You must be logged in to download the update.
Before applying the update, back up your existing installation, including all applications, configuration files, databases and database settings, and so on.

The References section of this erratum contains a download link for the update. You must be logged in to download the update.
The following conditions have to be met for an application compiled with OpenSSL to be vulnerable:

- the CA trusted by the system must issue or have issued certificates that don't include basic Key Usage extension.
- the CA certificates must not have path length constraint set to a value that would limit the certificate chain to just the subscriber certificates (i.e. CA certificate just above the subscriber cert must not have 0 as the path length constraint, and any CA above it must not have it increase by more than 1 for every level in the hierarchy)
- the attacker needs to have access to such subscriber certificate (without basic Key Usage and linking up to CAs without path length constraints or not effectively constraining certs issued by this certificate)
- the application under attack must use the X509_V_FLAG_X509_STRICT flag and must not set purpose for the certificate verification

if any of the above conditions are not met then the application compiled with OpenSSL is not vulnerable to the CVE.