Cisco has confirmed that attackers are actively exploiting a critical vulnerability in the software many businesses use to connect their offices together. The flaw, tracked as CVE-2026-76504 and rated 9.8 out of 10 on the CVSS severity scale, affects Cisco Catalyst SD-WAN Manager. It lets a remote attacker slip past a login check and gain administrator-level access to a protected management API. The U.S. Cybersecurity and Infrastructure Security Agency (CISA) has already added it to its Known Exploited Vulnerabilities (KEV) catalog and gave federal agencies until October 3, 2026 to fix it.