OpenC3 COSMOS: Stored, cross-user XSS via Telemetry screen BUTTON widget (CVE-2026-77394) | HOL Guard CVE

High · CVSS 7.6CVE-2026-77394

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

Answer in brief

CVE-2026-77394 records a High severity (CVSS 7.6) vulnerability in OpenC3 COSMOS: Stored, cross-user XSS via Telemetry screen BUTTON widget. The current sources do not mark it as known exploited. The current feed maps OpenC3/cosmos (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Sep 23, 2026Updated Sep 23, 2026Source checked Sep 23, 2026First seen by HOL Sep 23, 2026Material review Sep 23, 2026

Upstream Advisory

Key facts

Risk: High · CVSS 7.6
Exploitation: Not marked as known exploited
Affected software: 1 mapped package or product
Fix availability: Available

Why this deserves its current priority

CVSS is 7.6. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps OpenC3/cosmos (generic). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
OpenC3/cosmosgeneric	>=5.0.6 <7.3.0	7.3.0

Recommended response

Check inventory. Check lockfiles and deployed manifests for OpenC3/cosmos.
Review the reported fix. Update OpenC3/cosmos to 7.3.0 if you use the affected versions. Test the change in a non-production environment first.

Evidence timeline and material changes

Published upstream
Sep 23, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Sep 23, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Sep 23, 2026

Sources and claim methodology

Upstream source 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.

Quoted source text, attributed separately from HOL analysis.