CVE-2026-77602: OpenC3 COSMOS: Authenticated remote code execution via the user-writable config overlay (table definitions, cmd/tlm definitions, and script suites)

Should you act?

Critical, preconditions apply

Severe if exploited, but exploitation needs conditions that may not apply to you. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• Not in CISA KEV, but CISA’s SSVC assessment records a public proof-of-concept, so attack code exists.
• EPSS 0.6%, percentile 47: FIRST’s model estimates a 0.6% chance of exploitation activity in the next 30 days, higher than 47% of all scored CVEs (low). EPSS is a probability, not a verdict.
• Needs an account (low (any account)). Exposure depends on who can log in.
• Only applies if your dependency tree includes openc3 (RubyGems) >= 5.1.0, <= 7.2.1, fixed in 7.3.0. Check your lockfile, including transitive dependencies.

What it is

OpenC3 COSMOS provides the functionality needed to send commands to and receive data from one or more embedded systems. From 5.1.0 until 7.3.0, authenticated non-administrator users can write content under targetsmodified/ that is later executed by multiple configuration paths below the intended code-execution privilege tier. Table and command or telemetry definitions are processed through ConfigParser, PacketConfig, GENERICREADCONVERSION, or GENERICWRITECONVERSION, allowing ERB rendering or Ruby and Python evaluation, while openc3-cosmos-script-runner-api/scripts/runsuiteanalysis.rb executes suite procedure files through require. Storage uploads, screen saves, and script creation can place content in the overlay, and triggering table processing, a cmd/tlm reload, or suite analysis executes the content in cmd-tlm-api, decom microservices, or Script Runner with access to internal credentials and data. This issue is fixed in version 7.3.0.

From the GitHub advisory

Summary

COSMOS reads configuration from a user-writable overlay (targetsmodified/) before the read-only plugin-installed targets/ tree, and the config subsystem executes code on those files: ConfigParser renders every file as ERB by default, a GENERICREADCONVERSION / GENERICWRITECONVERSION block is evaluated as code by GenericConversion (Ruby and Python), and the Script Runner suite analysis requires a procedure file. An authenticated user can write into targetsmodified/ below the admin tier (the storage-upload endpoint exempts that area from the admin gate, and the screen-save endpoint stores its body verbatim there), so the same root cause is reachable through several features, each giving arbitrary code execution on a COSMOS server.

Three vulnerable routes were identified, all reachable by an authenticated non-admin user (in the open-source edition authorize ignores the permission string, so any authenticated user qualifies):

1. Table definitions (immediate). tables#generate|report|load reads a definition from targetsmodified/ and ERB-renders it and evaluates its GENERICCONVERSION block in the cmd-tlm-api container. 2. Command/telemetry definitions (persistent). A file written to targetsmodified/ /cmdtlm/ is overlaid by System.setuptargets and processed by PacketConfig in the decom/multi microservices: ERB-rendered in the Ruby implementation, and GENERIC-evaluated in both the Ruby and Python implementations (the Python ConfigParser does not run ERB). It executes on the next microservice (re)start. 3. Script Runner suites (immediate). A procedure written to targetsmodified/ /procedures/ is required by the suite analysis, reachable at the read-only scriptview tier through scripts#body and runningscript#show (the analysis subprocess is spawned when OPENC3SERVICEPASSWORD is configured, which it is in the shipped .env).

Details

Weakness type: CWE-94.

Product: openc3 (RubyGems) · Assigned by: GitHub_M · Published: 2026-09-23

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Privileges required: low (any account)
• User interaction: none
• Scope: changed (can affect other components)

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
• CISA SSVC assessment: exploitation poc, automatable no, technical impact total.
• FIRST EPSS (model of 2026-10-21): 0.57% probability of exploitation activity in the next 30 days; percentile 47.

Timeline

• 2026-09-23 — CVE record published by GitHub_M
• 2026-09-23 — GitHub-reviewed advisory GHSA-jjq7-m736-w977 published (critical)
• 2026-09-29 — CVE record last updated

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vulnerability records

1. GitHub Advisory GHSA-jjq7-m736-w977 github.com
2. CVE.org record CVE-2026-77602 cve.org
3. NVD entry CVE-2026-77602 nvd.nist.gov

Other references from the CVE record and advisory

1. github.com github.com
2. github.com github.com
3. github.com github.com
4. github.com github.com

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