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[ CVE-2026-77394 · Published 23 Sep 2026 ]

OpenC3 COSMOS: Stored, cross-user XSS via Telemetry screen BUTTON widget

CVSS 7.6 EPSS <1%Fix available

[ Why it matters ]Priority signals

  • Public proof-of-concept exploit exists (CISA SSVC)

[ Description ]Official description

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.

[ Fixes ]Fixes and patches

  • @openc3/vue-common 7.3.0Fixed version · GitHub Advisories · npm package @openc3/vue-common: upgrade to 7.3.0 or later (affected >= 5.0.6, <= 7.2.1)

[ Packages ]Affected open-source packages

[ References ]References