OpenC3 COSMOS: Self-XSS in the Command Sender

published 2026-04-22 6 mo ago modified 2026-10-26 13 d ago also EUVD-2026-27061 , GHSA-ffq5-qpvf-xq7x , PYSEC-2026-105

cvss: 4.6; version 3.1, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.2%; EPSS 0.2% chance of exploitation in 30 days, percentile 9%
public exploits: 0; none known

OpenC3 COSMOS provides the functionality needed to send commands to and receive data from one or more embedded systems. Prior to version 7.0.0, the Command Sender UI uses an unsafe eval() function on array-like command parameters, which allows a user-supplied payload to execute in the browser when sending a command. This creates a self-XSS risk because an attacker can trigger their own script execution in the victim’s session, if allowed to influence the array parameter input, for example via phishing. If successful, an attacker may read or modify data in the authenticated browser context, including session tokens in local storage. This issue has been patched in version 7.0.0.

Patch / fix

fixed in 3

rubygems openc3 7.0.0
pypi openc3 7.0.0
openc3 cosmos 7.0.0

CISA SSVC

Exploitation: Proof of concept is public
Automatable: no
Technical impact: partial
Assessed: 6 mo ago (2026-05-04)

Exploit prediction

0.20% chance of exploitation in the next 30 days, higher than 9% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

github.com https://github.com/OpenC3/cosmos/security/advisories/GHSA-ffq5-qpvf-xq7x referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by	version	score	vector
CNA	3.1	4.6	CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:L/I:L/A:N
GitHub	3.1	4.6	CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:L/I:L/A:N
OSV	3.1	4.6	CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:L/I:L/A:N

Affected packages

ecosystem	package	affected	fixed in
rubygems	openc3	<7.0.0	7.0.0
pypi	openc3	<7.0.0	7.0.0

Affected products

OpenC3 cosmos

Classification

Weakness

CWE-79 Improper Neutralization of Input During Web Page Generation

References

github.com /OpenC3/cosmos/security/advisories/GHSA-ffq5-qpvf-xq7x
exploit, web, vendor-advisory, evidence
nvd.nist.gov /vuln/detail/CVE-2026-42086
advisory
github.com /OpenC3/cosmos
package
github.com /pypa/advisory-database/tree/main/vulns/openc3/PYSEC-2026-105.yaml
web
github.com /rubysec/ruby-advisory-db/blob/master/gems/openc3/CVE-2026-42086.yml
web

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.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.

Summary