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Vulnerability · Published Sep 23, 2026 · Assigned by GitHub_M

CVE-2026-77394OpenC3 COSMOS: Stored, cross-user XSS via Telemetry screen BUTTON widget

High 7.6

In plain English

A high-severity cross-site scripting in cosmos from OpenC3. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 36% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)7.6High
Exploit odds (30 days)0.4%top 63.7% of all CVEs
Exploited in the wildNo reportsCISA SSVC: poc
Attack toolingNoneno public tooling known

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.

Affected packages & fixed versions

EcosystemPackageFixed inAdvisory
npm@openc3/vue-common7.3.0GHSA-gvf2-2rh5-mpgf

Affected products (as reported)

VendorProductVersions
OpenC3 cosmos >= 5.0.6, < 7.3.0

Weakness: CWE-79 · Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:L/A:N

References