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Fencer Vulns
high 7.6

CVE-2026-77394 json

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

published 2026-09-23 46 d ago modified 2026-09-23 46 d ago also GHSA-gvf2-2rh5-mpgf , EUVD-2026-85564

cvss
7.6
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.4%
EPSS 0.4% chance of exploitation in 30 days, percentile 36%
public exploits
0
none known

Summary

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.

Patch / fix

  • npm @openc3/vue-common 7.3.0

CISA SSVC

Exploitation
Proof of concept is public
Automatable
no
Technical impact
partial
Assessed
46 d ago

Exploit prediction

0.42% chance of exploitation in the next 30 days, higher than 36% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • github.com https://github.com/OpenC3/cosmos/security/advisories/GHSA-gvf2-2rh5-mpgf referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 3.1 7.6 CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:L/A:N
GitHub 3.1 7.6 CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:L/A:N

Affected packages

ecosystem package affected fixed in
npm @openc3/vue-common
>=5.0.6, <7.3.0
7.3.0

Affected products

  • OpenC3 cosmos

Classification

Weakness
  • CWE-79 Improper Neutralization of Input During Web Page Generation

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.