CVE-2026-42086 — openc3
MEDIUMCVE-2026-42086 is a medium-severity (CVSS 4.6) Cross-site Scripting (XSS) vulnerability in openc3. A fix is available for openc3 — see the affected versions and patch details below.
OpenC3 COSMOS: Self-XSS in the Command Sender
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-42086.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
Real-World Exposure
openc3💎openc3Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI, RubyGems packages — download data is not available via public APIs for these ecosystems.
Description
Summary
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.
Details
The unsafe eval() usage on user-supplied ARRAY parameters happens in convertToValue method in CommandSender.vue
PoC
- Using a drop-down form, choose any command that supports ARRAY parameters,
- Inside square brackets “[…]” place a JavaScript code to be executed
- Send command to CmdTlmServer using dedicated “Send” button
- Observe JavaScript code being executed in the current browser session context
Below example uses INST ARYCMD to execute simple JavaScript code snippet alert(“XSS”).
<img width="947" height="356" alt="image" src="https://github.com/user-attachments/assets/6fbdb6c9-616a-4268-bbb8-a8a1044437ad" />
Impact
Local JavaScript execution in the user's browser
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | openc3 | all versions | 7.0.0pip install --upgrade 'openc3==7.0.0' |
| 💎RubyGems | openc3 | all versions | 7.0.0bundle update openc3 --conservative |
Affected Products
cosmosopenc3Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for openc3, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update openc3 to 7.0.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-42086 is resolved across your whole dependency graph.
Workarounds
Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.
Frequently Asked Questions
Is CVE-2026-42086 in your dependencies?
Find it across PyPI, RubyGems, including transitive dependencies.