CVE-2024-5594: control channel: refuse control channel messages with nonprintable characters in them.

Security scope: a malicious openvpn peer can send garbage to openvpn log, or cause high CPU load.

References

• Release notes: https://www.mail-archive.com/openvpn-users@lists.sourceforge.net/msg07634.html
• CVE record: https://www.cve.org/CVERecord?id=CVE-2024-5594
• Reported by: Reynir Björnsson