Updated stunnel packages are now available for Red Hat Linux 7.1, 7.2, 7.3, and 8.0. These updates correct a potential vulnerability in stunnel's signal handling.
Stunnel is a wrapper for network connections. It can be used to tunnel an unencrypted network connection over a secure connection (encrypted using SSL or TLS) or to provide a secure means of connecting to services that do not natively support encryption. When configured to listen for incoming connections (instead of being invoked by xinetd), stunnel can be configured to either start a thread or a child process to handle each new connection. If Stunnel is configured to start a new child process to handle each connection, it will receive a SIGCHLD signal when that child exits. Stunnel versions prior to 4.04 would perform tasks in the SIGCHLD signal handler which, if interrupted by another SIGCHLD signal, could be unsafe. This could lead to a denial of service. All users are urged to upgrade to these errata packages, which modify stunnel's signal handler so that it is not vulnerable to this issue. NOTE: After upgrading, any instances of stunnel configured to run in daemon mode should be restarted, and any active network connections that are currently being serviced by stunnel should be terminated and reestablished.