A critical security flaw in Issabel Framework, a web-based framework for the open-source unified communications PBX software, has come under active exploitation.

The vulnerability in question is CVE-2026–89026 (CVSS v3.1 score: 9.8/CVSS v4.0 score: 9.3), which can allow an unauthenticated remote attacker to execute arbitrary operating system (OS) commands by taking advantage of a hard-coded JSON Web Token (JWT) signing key.

The Issabel Framework “contains a hard-coded HS256 JWT signing key in the pbxapi index.php file that is identical across every installation, allowing unauthenticated remote attackers to forge valid bearer tokens,” VulnCheck said in an alert.