CVE-2026-42086: Openc3 Cross-Site Scripting Vulnerability

MODERATE
Advisory Identifier: GHSA-ffq5-qpvf-xq7x
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CVSS 4.6
CWE-79
Published
Advisory Summary

CVE-2026-42086 is a MODERATE (CVSS 4.6) cross-site scripting vulnerability (CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')) affecting Openc3 libraries in the RubyGems ecosystem. The issue involves openc3 cosmos is vulnerable to self-xss through the command sender. Remediation is available by upgrading affected packages to version 7.0.0.

CVE-2026-42086 at a Glance

CVE Identifier CVE-2026-42086
GHSA Identifier GHSA-ffq5-qpvf-xq7x
Severity MODERATE
CVSS v3.1 Base Score 4.6
CWE Classification CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
Affected Product Openc3
Package Ecosystem RubyGems
Published Date
Last Updated

Security Impact

CVSS: 4.6

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:L/I:L/A:N).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required Low (PR:L)
User Interaction Required (UI:R)
Scope Unchanged (S:U)
Confidentiality Low (C:L)
Integrity Low (I:L)
Availability None (A:N)

How to Fix CVE-2026-42086

To remediate this vulnerability, upgrade all affected Openc3 dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

openc3 fixed: 7.0.0 
Upgrade openc3 to 7.0.0
openc3 fixed: 7.0.0 
pip install openc3>=7.0.0
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

inspect dependencies for openc3

How to Check if You Are Affected

To determine whether your application is affected by CVE-2026-42086, inspect your project dependencies for Openc3:

inspect dependencies for openc3

Analyze the terminal output to locate any version of Openc3 in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 7.0.0), your application is affected.

Note: Verify declared build manifests and deployed runtime container environments.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting'), where the product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users. In Openc3, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

### 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](https://github.com/OpenC3/cosmos/blob/main/openc3-cosmos-init/plugins/packages/openc3-cosmos-tool-cmdsender/src/tools/CommandSender/CommandSender.vue) ### PoC 1. Using a drop-down form, choose any command that supports ARRAY parameters, 2. Inside square brackets “[…]” place a JavaScript code to be executed 3. Send command to CmdTlmServer using dedicated “Send” button 4. 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" /> <img width="942" height="545" alt="image" src="https://github.com/user-attachments/assets/4df24353-aea0-4aa0-adcf-b7c7e387dc83" /> ### Impact Local JavaScript execution in the user's browser

CVE-2026-42086 Affected Openc3 Versions

2 component(s)
Fixed Versions:
7.0.0
Product / Package Ecosystem Affected Versions Fixed Version
openc3
gem/openc3
RubyGems
< 7.0.0
7.0.0
openc3
pypi/openc3
PyPI
< 7.0.0
7.0.0

References

GitHub Advisory / Wiki ADVISORY
https://github.com/OpenC3/cosmos/security/advisories/GHSA-ffq5-qpvf-xq7x
NVD — CVE-2026-42086 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-42086
Openc3 Source Repository REPOSITORY
https://github.com/OpenC3/cosmos
Openc3 Source Repository REPOSITORY
https://github.com/pypa/advisory-database/tree/main/vulns/openc3/PYSEC-2026-105.yaml
Openc3 Source Repository REPOSITORY
https://github.com/rubysec/ruby-advisory-db/blob/master/gems/openc3/CVE-2026-42086.yml

Frequently Asked Questions

What is CVE-2026-42086?
CVE-2026-42086 is a security vulnerability in Openc3 involving OpenC3 COSMOS is Vulnerable to Self-XSS Through the Command Sender under CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting').
Which Openc3 versions are affected?
Affected versions include releases prior to 7.0.0 across affected packages: openc3.
What version fixes CVE-2026-42086?
Upgrading to 7.0.0 (or the latest patched release for your respective branch) resolves the vulnerability.
Is openc3 affected?
Yes, openc3 is affected in releases prior to 7.0.0. Upgrade your dependency to 7.0.0 or later.
What is the CVSS score of CVE-2026-42086?
CVE-2026-42086 has a CVSS v3.1 base score of 4.6 (MODERATE) with vector string CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:L/I:L/A:N.
What CWE is associated with CVE-2026-42086?
CVE-2026-42086 is classified under CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') (The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.).
How can I check RubyGems dependencies for CVE-2026-42086?
Run the dependency tree command: 'inspect dependencies for openc3'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-ffq5-qpvf-xq7x",
  "modified" : "2026-05-29T21:46:39Z",
  "published" : "2026-04-22T22:22:28Z",
  "aliases" : [ "CVE-2026-42086" ],
  "summary" : "OpenC3 COSMOS is Vulnerable to Self-XSS Through the Command Sender",
  "details" : "### Summary\nThe 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.\n\n### Details\nThe unsafe `eval()`  usage on user-supplied ARRAY parameters happens in `convertToValue` method in [CommandSender.vue](https://github.com/OpenC3/cosmos/blob/main/openc3-cosmos-init/plugins/packages/openc3-cosmos-tool-cmdsender/src/tools/CommandSender/CommandSender.vue)\n\n### PoC\n1.\tUsing a drop-down form, choose any command that supports ARRAY parameters,\n2.\tInside square brackets “[…]” place a JavaScript code to be executed\n3.\tSend command to CmdTlmServer using dedicated “Send” button \n4.\tObserve JavaScript code being executed in the current browser session context\n\nBelow example uses `INST ARYCMD` to execute simple JavaScript code snippet `alert(“XSS”)`.\n<img width=\"947\" height=\"356\" alt=\"image\" src=\"https://github.com/user-attachments/assets/6fbdb6c9-616a-4268-bbb8-a8a1044437ad\" />\n\n<img width=\"942\" height=\"545\" alt=\"image\" src=\"https://github.com/user-attachments/assets/4df24353-aea0-4aa0-adcf-b7c7e387dc83\" />\n\n### Impact\nLocal JavaScript execution in the user's browser",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:L/I:L/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "RubyGems",
      "name" : "openc3"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "7.0.0"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "openc3"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "7.0.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/OpenC3/cosmos/security/advisories/GHSA-ffq5-qpvf-xq7x"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-42086"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/OpenC3/cosmos"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/pypa/advisory-database/tree/main/vulns/openc3/PYSEC-2026-105.yaml"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/rubysec/ruby-advisory-db/blob/master/gems/openc3/CVE-2026-42086.yml"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-79" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-04-22T22:22:28Z",
    "nvd_published_at" : "2026-05-04T18:16:30Z"
  }
}