hunt-rce

## Crown Jewel Targets

RCE vulnerabilities command the highest payouts in bug bounty programs because they grant attackers direct execution control over target infrastructure. The highest-value targets are:

**Highest-paying asset types:**
- **Enterprise server products** (GitHub Enterprise Server, self-hosted GitLab) — privilege escalation chains from low-privileged console roles to root SSH access consistently pay critical/high
- **Supply chain / package registries** — dependency confusion attacks against npm, PyPI, etc. hit critical severity across every major program
- **Cloud-native infrastructure** — exposed Kubernetes API servers, ingress controllers, and misconfiqured CI/CD pipelines
- **Mobile app backends and OAuth flows** — where server-side processing of attacker-controlled data meets execution contexts
- **Admin/management consoles** — template injection in configuration panels reaches root with a single payload

**Why this class pays most:**
- Blast radius is infrastructure-wide, not user-scoped
- Proof-of-concept is unambiguous — shell output is undeniable
- Fix requires architectural changes, not just a patch
- Programs cannot afford false negatives on RCE

---

## Attack Surface Signals

### URL Patterns
```
/management-console/*
/admin/settings/*
/api/v*/exec
/api/v*/run
/webhook/*
/_internal/*
/import?url=
/render?template=
/preview?format=
```

### Response Headers / Tech Stack Signals
```
X-Powered-By: Express          # Node.js — npm dependency surface
X-Powered-By: Phusion Passenger
Server: nginx (ingress-nginx)  # Kubernetes ingress — path field injection
X-Runtime: Ruby                # Rails ActiveStorage, RDoc, REXML attack surface
Content-Type: application/yaml # YAML parsers (SnakeYAML, Psych) — deserialization
X-GitHub-Enterprise-Version    # GHAS — nomad template, collectd, syslog-ng injection
```

### JavaScript / Frontend Signals
```javascript
// Look for these patterns in JS bundles
fetch('/api/exec', {method:'POST', body: cmd})
eval(userInput)
new Function(userInput)
document.write(unsafeData)
window.location = userControlled  // URL scheme bypass → JS execution
```

### Tech Stack Signals
| Signal | RCE Vector |
|--------|-----------|
| `nomad` in config UI | Template injection → `{{ ... }}` |
| `syslog-ng` config editable | Config injection → `program()` destination |
| `collectd` config editable | Plugin exec injection |
| `SnakeYAML` in classpath | `!!javax.script.ScriptEngineManager [...]` |
| npm `package.json` internal scope | Dependency confusion |
| ingress-nginx annotations | Path field regex bypass |

---

## Step-by-Step Hunting Methodology

1. **Map the execution contexts first.** Before testing payloads, identify everywhere user-controlled input touches an execution layer: template engines, shell commands, YAML parsers, file paths used in operations, package resolution, and configuration files.

2. **Enumerate admin/management interfaces.** Crawl for `/management-console`, `/admin`, `/_internal`, `/setup`, `/config`. These surfaces are lower-auth and higher-privilege — the GHES cluster produced 6 separate RCEs from one console role.

3. **Check template injection in every config field.** In any management UI that accepts free-form configuration (log destinations, notification formats, proxy settings), submit `{{7*7}}`, `${7*7}`, `<%= 7*7 %>`. Look for `49` in responses, logs, or DNS callbacks.

4. **Test YAML/XML/serialized input for code execution.** Any endpoint accepting `Content-Type: application/yaml` or `application/xml`:
   - SnakeYAML: submit `!!javax.script.ScriptEngineManager` gadget
   - Ruby YAML: submit `!ruby/object:Gem::Installer` gadget
   - REXML: submit billion-laughs / quadratic blowup XML

5. **Hunt dependency confusion.** For every npm/pip/gem internal package name visible in JS bundles, error messages, or `package.json` in public repos — register a higher-versioned package on the public registry pointing to a canary callback.

6. **Check file path operations for traversal → execution.** ActiveStorage, file upload handlers, symlink operations: submit `../../../etc/cron.d/shell` as filename. Confirm write then trigger execution.

7. **Audit Kubernetes/cloud-native surfaces.** Run `kubectl` against any exposed API server. Check ingress annotations, especially `nginx.ingress.kubernetes.io/configuration-snippet` and `spec.rules.http.paths.path` for Lua/regex injection.

8. **Test OAuth redirect URI and URL scheme handlers.** Mobile apps processing `javascript:` or `intent://` URIs via OAuth redirect may execute JavaScript. Try `javascript:alert(document.cookie)` and custom scheme URIs.

9. **Verify with out-of-band callbacks.** Never rely solely on visible output. Use Burp Collaborator, interactsh, or `canarytokens.org` DNS tokens. Blind RCE is common in backend processors.

10. **Chain privileges.** A low-severity misconfiguration (editor role, CSRF, path traversal) combined with an RCE primitive equals critical. Always ask: "what can I reach from here?"

---

## Payload & Detection Patterns

### Template Injection Probes
```
# Generic polyglot — works across Jinja2, Twig, Freemarker, Pebble, Velocity
{{7*7}}${7*7}#{7*7}<%= 7*7 %>*{7*7}
{{'7'*7}}
{{config}}
{{self._TemplateReference__context.cycler.__init__.__globals__.os.popen('id').read()}}

# Nomad template injection (Go text/template)
{{ env "NOMAD_SECRET_ID" }}
{{ with secret "secret/data/prod" }}{{ .Data.password }}{{ end }}
{{ runscript "id" }}
```

### Apache HTTP Server alias path traversal (CVE-2021-41773 / CVE-2021-42013)

Path normalization bug in Apache 2.4.49 (and the 2.4.50 patch-bypass) lets an attacker escape DocumentRoot via dot-encoded segments **through configured alias paths**. The same primitive yields very different impact depending on which alias accepts the traversal:

- Alias without `Options +ExecCGI` (e.g. `/icons/`) → arbitrary file read only
- Alias with `Options +ExecCGI` (e.g. `/cgi-bin/`) → arbitrary code execution

**Version fingerprint