WP-CLI is the command-line interface for WordPress. 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. 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. 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.