CVE-2026-77394

HIGH CVSS 3.1: 7.6 EPSS 0.39%
Updated Sep 23, 2026
OpenC3
Parameter Value
CVSS 7.6 (HIGH)
Fixed In 7.3.0
Type CWE-79 (Cross-Site Scripting (XSS))
Vendor OpenC3
Public PoC No

OpenC3 COSMOS provides the functionality needed to send commands to and receive data from one or more embedded systems. From 5.0.6 until 7.3.0, an authenticated actor with system_set permission can store a shared screen through POST /openc3-api/screen whose BUTTON widget action is evaluated by openc3-cosmos-init/plugins/packages/openc3-vue-common/src/widgets/ButtonWidget.vue in another operator's browser session when the button is activated. The stored script runs in the COSMOS origin and can read localStorage.openc3Token, allowing theft of the victim's bearer token, account takeover, and actions with the victim's privileges.

The permissive content security policy contributes to execution but is not the primary root cause. This issue is fixed in version 7.3.0.

Attack Parameters

Attack Vector
Network
Can be exploited remotely
Attack Complexity
Low
Easy to exploit
Privileges Required
Low
Basic privileges needed
User Interaction
Required
User action required

Impact Assessment

Confidentiality
High
Complete data leak
Integrity
Low
Partial data modification
Availability
None
No disruption

CVSS Vector v3.1