CVE-2021-29504: Improper Certificate Validation in WP-CLI framework

Impact

An improper error handling in HTTPS requests management in WP-CLI version 0.12.0 and later allows remote attackers able to intercept the communication to remotely disable the certificate verification on WP-CLI side, gaining full control over the communication content, including the ability to impersonate update servers and push malicious updates towards WordPress instances controlled by the vulnerable WP-CLI agent, or push malicious updates toward WP-CLI itself.

Patches

The vulnerability stems from the fact that the default behavior of WP_CLI\Utils\http_request() when encountering a TLS handshake error is to disable certificate validation and retry the same request.

The default behavior has been changed with version 2.5.0 of WP-CLI and the wp-cli/wp-cli framework (via https://github.com/wp-cli/wp-cli/pull/5523) so that the WP_CLI\Utils\http_request() method accepts an $insecure option that is false by default and consequently that a TLS handshake failure is a hard error by default. This new default is a breaking change and ripples through to all consumers of WP_CLI\Utils\http_request(), including those in separate WP-CLI bundled or third-party packages.

https://github.com/wp-cli/wp-cli/pull/5523 has also added an --insecure flag to the cli update command to counter this breaking change.

Subsequent PRs on the command repositories have added an --insecure flag to the appropriate commands on the following repositories to counter the breaking change:

• https://github.com/wp-cli/config-command/pull/128
• https://github.com/wp-cli/core-command/pull/186
• https://github.com/wp-cli/extension-command/pull/287
• https://github.com/wp-cli/checksum-command/pull/86
• https://github.com/wp-cli/package-command/pull/138

Workarounds

There is no direct workaround for the default insecure behavior of wp-cli/wp-cli versions before 2.5.0.

The workaround for dealing with the breaking change in the commands directly affected by the new secure default behavior is to add the --insecure flag to manually opt-in to the previous insecure behavior.

References

• CWE: Improper Certificate Validation

For more information

If you have any questions or comments about this advisory:

• Join the #cli channel in the WordPress.org Slack to ask questions or provide feedback.